Nakagawa, Kouichi; Minakawa, Satoko; Sawamura, Daisuke; Hara, Hideyuki
2017-01-01
Continuous wave electron paramagnetic resonance (CW EPR) and X-band (9 GHz) EPR imaging (EPRI) were used to nondestructively investigate the possible differentiation between malignant melanoma (MM) and nevus pigmentosus (NP) melanin radicals in paraffin-embedded specimens. The EPR spectra of both samples were analyzed using linewidth, spectral pattern, and X-band EPRI. The CW-EPR spectra of the MM showed an additional signal overlap. Eumelanin- and pheomelanin-related radicals were observed in the MM specimens. The EPR results revealed that the peak-to-peak linewidths (ΔH pp ) of paraffin-embedded MM and NP samples were 0.65 ± 0.01 and 0.69 ± 0.01 mT, respectively. The g-value was 2.005 for both samples. Moreover, the two-dimensional (2D) EPRI of the MM showed different signal intensities at the different tumor stages, unlike the NP, which displayed fewer variations in signal intensity. Thus, the present results suggest that EPR and 2D EPRI can be useful for characterization of the two melanin radicals in the MM and for determination of their size and concentration.
Nakagawa, Kouichi; Epel, Boris
2017-03-01
This study investigated the location and distribution of paramagnetic species in apple seeds using electron paramagnetic resonance (EPR) and X-band (9 GHz) EPR imaging (EPRI). EPR primarily detected two paramagnetic species per measured seed. These two different radical species were assigned as stable radicals and Mn 2+ species based on the g values and hyperfine components. The signal from the stable radical was noted at g ≈ 2.00 and was strong and relatively stable. The subsequent noninvasive EPRI of the radical present in each seed revealed that the stable radicals were located primarily in the seed coat, with very few radicals observed in the cotyledon of the seed. These results indicate that the stable radical species were only found within the seed coat, and few radical species were found in other seed parts.
NASA Astrophysics Data System (ADS)
Yordanov, Nicola D.; Aleksieva, Katerina
2004-01-01
X- and Q-band EPR studies after γ-irradiation of some dry spices and aromatic herbs are reported. Before irradiation all samples show only one singlet line in X-band EPR, whereas the Q-band EPR spectrum of the same samples is a superposition of two individual spectra—one corresponding to the above EPR signal, with an anisotropic spectrum, and a second one consisting of six lines due to the Mn 2+ naturally present in plants. The radiation induced EPR signal due to cellulose free radicals was not detected after γ-irradiation, but only the increase of the natural signal present before the irradiation. The fading kinetic of this EPR signal was monitored in three cases—when samples were kept in plastic bags without any special conditioning after irradiation, when samples were covered with paraffin before irradiation and when samples were dried at 60°C for 1 h before irradiation. The studies show that stability of radiation induced EPR signals decreases in the order of: paraffin covered > heated before irradiation > kept at room conditions. The two EPR spectra in the Q-band—one with radiation dependent intensity and a second due to Mn 2+, which is radiation independent allow identification of previous radiation treatment based on the fact that Mn 2+ quantity in the sample is constant whereas the quantity of radiation-induced free radicals is temperature dependent. It was found that for irradiated samples the ratio between EPR intensity of the free radicals and that of Mn 2+ before and after heating decreases with 50-60% whereas for non-irradiated samples it is ca. 10-15%.
Yano, Junko; Sauer, Kenneth; Girerd, Jean-Jacques; Yachandra, Vittal K
2004-06-23
The anisotropic g and hyperfine tensors of the Mn di-micro-oxo complex, [Mn(2)(III,IV)O(2)(phen)(4)](PF(6))(3).CH(3)CN, were derived by single-crystal EPR measurements at X- and Q-band frequencies. This is the first simulation of EPR parameters from single-crystal EPR spectra for multinuclear Mn complexes, which are of importance in several metalloenzymes; one of them is the oxygen-evolving complex in photosystem II (PS II). Single-crystal [Mn(2)(III,IV)O(2)(phen)(4)](PF(6))(3).CH(3)CN EPR spectra showed distinct resolved (55)Mn hyperfine lines in all crystal orientations, unlike single-crystal EPR spectra of other Mn(2)(III,IV) di-micro-oxo bridged complexes. We measured the EPR spectra in the crystal ab- and bc-planes, and from these spectra we obtained the EPR spectra of the complex along the unique a-, b-, and c-axes of the crystal. The crystal orientation was determined by X-ray diffraction and single-crystal EXAFS (Extended X-ray Absorption Fine Structure) measurements. In this complex, the three crystallographic axes, a, b, and c, are parallel or nearly parallel to the principal molecular axes of Mn(2)(III,IV)O(2)(phen)(4) as shown in the crystallographic data by Stebler et al. (Inorg. Chem. 1986, 25, 4743). This direct relation together with the resolved hyperfine lines significantly simplified the simulation of single-crystal spectra in the three principal directions due to the reduction of free parameters and, thus, allowed us to define the magnetic g and A tensors of the molecule with a high degree of reliability. These parameters were subsequently used to generate the solution EPR spectra at both X- and Q-bands with excellent agreement. The anisotropic g and hyperfine tensors determined by the simulation of the X- and Q-band single-crystal and solution EPR spectra are as follows: g(x) = 1.9887, g(y) = 1.9957, g(z) = 1.9775, and hyperfine coupling constants are A(III)(x) = |171| G, A(III)(y) = |176| G, A(III)(z) = |129| G, A(IV)(x) = |77| G, A
Multifrequency EPR study on freeze-dried fruits before and after X-ray irradiation
NASA Astrophysics Data System (ADS)
Yordanov, N. D.; Aleksieva, K.; Dimitrova, A.; Georgieva, L.; Tzvetkova, E.
2006-09-01
X-, K- and Q-band EPR studies on lyophilized whole pulp parts of blue plum, apricot, peach, melon as well as achens and pulp separately of strawberry before and after X-ray irradiation are reported. Before irradiation all samples show in X band a weak singlet EPR line with g=2.0030±0.0005, except melon, which is EPR silent. Immediately after irradiation all samples exhibit complex fruit-depending spectra, which decay with time and change to give, in ca. 50 days, an asymmetric singlet EPR line with g=2.0041±0.0005. Only apricot pulp gave a typical "sugar-like" EPR spectrum. Singlet EPR lines recorded after irradiation in X -band are K- and Q-band resolved as typical anisotropic EPR spectra with g=2.0023±0.0003 and g⊥=2.0041±0.0005. In addition, K- and Q-band EPR spectra of all samples show a superposition with the six EPR lines of Mn 2+ naturally present in the fruits. The saturation behavior of the EPR spectra of achens of lyophilized and fresh strawberry is also studied. The differences in g factors of samples before and after X-ray irradiation might be used for the identification of radiation processing of fruits in the case of pulp and the differences in the EPR saturation behavior might be used for the achens of strawberry.
Using spin-label W-band EPR to study membrane fluidity profiles in samples of small volume
NASA Astrophysics Data System (ADS)
Mainali, Laxman; Hyde, James S.; Subczynski, Witold K.
2013-01-01
Conventional and saturation-recovery (SR) EPR at W-band (94 GHz) using phosphatidylcholine spin labels (labeled at the alkyl chain [n-PC] and headgroup [T-PC]) to obtain profiles of membrane fluidity has been demonstrated. Dimyristoylphosphatidylcholine (DMPC) membranes with and without 50 mol% cholesterol have been studied, and the results have been compared with similar studies at X-band (9.4 GHz) (L. Mainali, J.B. Feix, J.S. Hyde, W.K. Subczynski, J. Magn. Reson. 212 (2011) 418-425). Profiles of the spin-lattice relaxation rate (T1-1) obtained from SR EPR measurements for n-PCs and T-PC were used as a convenient quantitative measure of membrane fluidity. Additionally, spectral analysis using Freed's MOMD (microscopic-order macroscopic-disorder) model (E. Meirovitch, J.H. Freed J. Phys. Chem. 88 (1984) 4995-5004) provided rotational diffusion coefficients (R⊥ and R||) and order parameters (S0). Spectral analysis at X-band provided one rotational diffusion coefficient, R⊥. T1-1, R⊥, and R|| profiles reflect local membrane dynamics of the lipid alkyl chain, while the order parameter shows only the amplitude of the wobbling motion of the lipid alkyl chain. Using these dynamic parameters, namely T1-1, R⊥, and R||, one can discriminate the different effects of cholesterol at different depths, showing that cholesterol has a rigidifying effect on alkyl chains to the depth occupied by the rigid steroid ring structure and a fluidizing effect at deeper locations. The nondynamic parameter, S0, shows that cholesterol has an ordering effect on alkyl chains at all depths. Conventional and SR EPR measurements with T-PC indicate that cholesterol has a fluidizing effect on phospholipid headgroups. EPR at W-band provides more detailed information about the depth-dependent dynamic organization of the membrane compared with information obtained at X-band. EPR at W-band has the potential to be a powerful tool for studying membrane fluidity in samples of small volume, ˜30 n
DAC-board based X-band EPR spectrometer with arbitrary waveform control
NASA Astrophysics Data System (ADS)
Kaufmann, Thomas; Keller, Timothy J.; Franck, John M.; Barnes, Ryan P.; Glaser, Steffen J.; Martinis, John M.; Han, Songi
2013-10-01
We present arbitrary control over a homogenous spin system, demonstrated on a simple, home-built, electron paramagnetic resonance (EPR) spectrometer operating at 8-10 GHz (X-band) and controlled by a 1 GHz arbitrary waveform generator (AWG) with 42 dB (i.e. 14-bit) of dynamic range. Such a spectrometer can be relatively easily built from a single DAC (digital to analog converter) board with a modest number of stock components and offers powerful capabilities for automated digital calibration and correction routines that allow it to generate shaped X-band pulses with precise amplitude and phase control. It can precisely tailor the excitation profiles "seen" by the spins in the microwave resonator, based on feedback calibration with experimental input. We demonstrate the capability to generate a variety of pulse shapes, including rectangular, triangular, Gaussian, sinc, and adiabatic rapid passage waveforms. We then show how one can precisely compensate for the distortion and broadening caused by transmission into the microwave cavity in order to optimize corrected waveforms that are distinctly different from the initial, uncorrected waveforms. Specifically, we exploit a narrow EPR signal whose width is finer than the features of any distortions in order to map out the response to a short pulse, which, in turn, yields the precise transfer function of the spectrometer system. This transfer function is found to be consistent for all pulse shapes in the linear response regime. In addition to allowing precise waveform shaping capabilities, the spectrometer presented here offers complete digital control and calibration of the spectrometer that allows one to phase cycle the pulse phase with 0.007° resolution and to specify the inter-pulse delays and pulse durations to ⩽250 ps resolution. The implications and potential applications of these capabilities will be discussed.
NASA Astrophysics Data System (ADS)
Veber, Sergey L.; Tumanov, Sergey V.; Fursova, Elena Yu.; Shevchenko, Oleg A.; Getmanov, Yaroslav V.; Scheglov, Mikhail A.; Kubarev, Vitaly V.; Shevchenko, Daria A.; Gorbachev, Iaroslav I.; Salikova, Tatiana V.; Kulipanov, Gennady N.; Ovcharenko, Victor I.; Fedin, Matvey V.
2018-03-01
Electron Paramagnetic Resonance (EPR) station at the Novosibirsk Free Electron Laser (NovoFEL) user facility is described. It is based on X-band (∼9 GHz) EPR spectrometer and operates in both Continuous Wave (CW) and Time-Resolved (TR) modes, each allowing detection of either direct or indirect influence of high-power NovoFEL light (THz and mid-IR) on the spin system under study. The optics components including two parabolic mirrors, shutters, optical chopper and multimodal waveguide allow the light of NovoFEL to be directly fed into the EPR resonator. Characteristics of the NovoFEL radiation, the transmission and polarization-retaining properties of the waveguide used in EPR experiments are presented. The types of proposed experiments accessible using this setup are sketched. In most practical cases the high-power radiation applied to the sample induces its rapid temperature increase (T-jump), which is best visible in TR mode. Although such influence is a by-product of THz radiation, this thermal effect is controllable and can deliberately be used to induce and measure transient signals of arbitrary samples. The advantage of tunable THz radiation is the absence of photo-induced processes in the sample and its high penetration ability, allowing fast heating of a large portion of virtually any sample and inducing intense transients. Such T-jump TR EPR spectroscopy with THz pulses has been previewed for the two test samples, being a useful supplement for the main goals of the created setup.
Veber, Sergey L; Tumanov, Sergey V; Fursova, Elena Yu; Shevchenko, Oleg A; Getmanov, Yaroslav V; Scheglov, Mikhail A; Kubarev, Vitaly V; Shevchenko, Daria A; Gorbachev, Iaroslav I; Salikova, Tatiana V; Kulipanov, Gennady N; Ovcharenko, Victor I; Fedin, Matvey V
2018-03-01
Electron Paramagnetic Resonance (EPR) station at the Novosibirsk Free Electron Laser (NovoFEL) user facility is described. It is based on X-band (∼9 GHz) EPR spectrometer and operates in both Continuous Wave (CW) and Time-Resolved (TR) modes, each allowing detection of either direct or indirect influence of high-power NovoFEL light (THz and mid-IR) on the spin system under study. The optics components including two parabolic mirrors, shutters, optical chopper and multimodal waveguide allow the light of NovoFEL to be directly fed into the EPR resonator. Characteristics of the NovoFEL radiation, the transmission and polarization-retaining properties of the waveguide used in EPR experiments are presented. The types of proposed experiments accessible using this setup are sketched. In most practical cases the high-power radiation applied to the sample induces its rapid temperature increase (T-jump), which is best visible in TR mode. Although such influence is a by-product of THz radiation, this thermal effect is controllable and can deliberately be used to induce and measure transient signals of arbitrary samples. The advantage of tunable THz radiation is the absence of photo-induced processes in the sample and its high penetration ability, allowing fast heating of a large portion of virtually any sample and inducing intense transients. Such T-jump TR EPR spectroscopy with THz pulses has been previewed for the two test samples, being a useful supplement for the main goals of the created setup. Copyright © 2018 Elsevier Inc. All rights reserved.
Stability of X-band EPR signals from fingernails under vacuum storage.
Sholom, Sergey; McKeever, Stephen
2017-12-01
EPR signals of different origin have been tested in human finger- and toe-nails with an X-band EPR technique for different conditions of nail storage. Three different signals were identified, namely a singlet at g=2.005, a doublet at g=2.004 with a splitting constant A=1.8 mT, and an anisotropic signal at g1=2.057, g2=2.029 and g3=2.003 (positions of local extrema). All EPR spectra from nails, whether irradiated or mechanically stressed, can be described as a superposition of these three signals. The singlet is responsible for the background signal (BG), is the main component of radiation-induced signals (RIS) for low doses (100 Gy or lower) and also contributes to mechanically-induced signals (MIS). This signal is quite stable under vacuum storage, but can be reduced almost to zero by soaking in water. The behavior of this signal under ambient conditions depends on many factors, such as absorbed dose, air humidity, and ambient illumination intensity at the place of storage. The doublet arises after exposure of nails to high (few hundreds Gy and higher) doses or after mechanical stress of samples. Depending on how this signal was obtained, it may have bulk or surface locations with quite different stability properties. The surface-located doublet (generated on the nail edges during cutting or clipping) is quite unstable and decays over about two hours for samples stored at ambient conditions and within several seconds for samples immersed in water. The volume-distributed doublet decays within a few minutes in water, several hours at ambient conditions and several days in vacuum. The anisotropic signal may also be generated by both ionizing radiation and mechanical stress; this signal is quite stable in vacuum and decays over several days at ambient conditions or a few tens of minutes in water. The reference lines for the above-described three EPR signals were obtained and a procedure of spectra deconvolution was developed and tested on samples exposed to both
L Band EPR Tooth Dosimetry for Heavy Ion Irradiation
Yamaguchi, Ichiro; Sato, Hitoshi; Kawamura, Hiraku; Hamano, Tsuyoshi; Yoshii, Hiroshi; Suda, Mitsuru; Miyake, Minoru; Kunugita, Naoki
2016-01-01
Electron Paramagnetic Resonance (EPR) tooth dosimetry is being developed as a device to rapidly assess large populations that were potentially exposed to radiation during a major radiation accident or terrorist event. While most exposures are likely to be due to fallout and therefore involve low linear energy transfer (LET) radiation, there is also a potential for exposures to high LET radiation, for which the effect on teeth has been less well characterized by EPR. Therefore, the aim of this paper is to acquire fundamental response curves for high LET radiation in tooth dosimetry using L band EPR. For this purpose, we exposed human teeth to high energy carbon ions using the heavy ion medical accelerator in Chiba at the National Institute of Radiological Sciences. The primary findings were that EPR signals for carbon ion irradiation were about one-tenth the amplitude of the response to the same dose of 150 kVp X-rays. PMID:27542817
Kittell, Aaron W.; Hustedt, Eric J.; Hyde, James S.
2014-01-01
Site-directed spin-labeling electron paramagnetic resonance (SDSL EPR) provides insight into the local structure and motion of a spin probe strategically attached to a molecule. When a second spin is introduced to the system, macromolecular information can be obtained through measurement of inter-spin distances either by continuous wave (CW) or pulsed electron double resonance (ELDOR) techniques. If both methodologies are considered, inter-spin distances of 8 to 80 Å can be experimentally determined. However, there exists a region at the upper limit of the conventional X-band (9.5 GHz) CW technique and the lower limit of the four-pulse double electron-electron resonance (DEER) experiment where neither method is particularly reliable. The work presented here utilizes L-band (1.9 GHz) in combination with non-adiabatic rapid sweep (NARS) EPR to address this opportunity by increasing the upper limit of the CW technique. Because L-band linewidths are three to seven times narrower than those at X-band, dipolar broadenings that are small relative to the X-band inhomogeneous linewidth become observable, but the signal loss due to the frequency dependence of the Boltzmann factor, has made L-band especially challenging. NARS has been shown to increase sensitivity by a factor of five, and overcomes much of this loss, making L-band distance determination more feasible [1]. Two different systems are presented and distances of 18–30 Å have been experimentally determined at physiologically relevant temperatures. Measurements are in excellent agreement with a helical model and values determined by DEER. PMID:22750251
Ramos, Paweł; Pilawa, Barbara
The effect of UVA (315-400 nm) irradiation on Echinaceae purpureae interactions with free radicals was examined by the use of electron paramagnetic resonance (EPR) spectroscopy. The changes of antioxidant properties of E. purpureae with time of UV irradiation from 10 to 110 min (10 min steps) were determined. DPPH as the paramagnetic reference was used in this study. Changes of EPR signals of the reference after interactions with nonirradiated and UV-irradiated E. purpureae were detected. Interactions of the tested E. purpureae samples caused decrease of the EPR signal of DPPH as the result of its antioxidant properties. The decrease of the amplitude of EPR line of DPPH was lower for interactions with UV-irradiated E. purpureae . EPR examination confirmed antioxidant properties of E. purpureae . The weaker antioxidant properties of E. purpureae after UV irradiation were pointed out. E. purpureae should be storage in the dark. The tests bring to light usefulness of electron paramagnetic resonance with microwave frequency of 9.3 GHz (an X-band) in examination of storage conditions of pharmacological herbs.
NASA Astrophysics Data System (ADS)
Misra, Sushil K.; Andronenko, S. I.; Srinivasa Rao, S.; Chess, Jordan; Punnoose, A.
2015-11-01
EPR investigations on two types of dilute magnetic semiconductor (DMS) ZnO nanoparticles doped with 0.5-10% Co2+ ions, prepared by two chemical hydrolysis methods, using: (i) diethylene glycol ((CH2CH2OH)2O) (NC-rod-like samples), and (ii) denatured ethanol (CH3CH2OH) solutions (QC-spherical samples), were carried out at X-band (9.5 GHz) at 5 K. The analysis of EPR data for NC samples revealed the presence of several types of EPR lines: (i) two types, intense and weak, of high-spin Co2+ ions in the samples with Co concentration >0.5%; (ii) surface oxygen vacancies, and (iii) a ferromagnetic resonance (FMR) line. QC samples exhibit an intense FMR line and an EPR line due to high-spin Co2+ ions. FMR line is more intense, than the corresponding line exhibited by NC samples. These EPR spectra varied for sample with different doping concentrations. The magnetic states of these samples as revealed by EPR spectra, as well as the origin of ferromagnetism DMS samples are discussed.
Miyake, Minoru; Nakai, Yasuhiro; Yamaguchi, Ichiro; Hirata, Hiroshi; Kunugita, Naoki; Williams, Benjamin B.; Swartz, Harold M.
2016-01-01
The aim of this study was to make direct measurements of the possible radiation-induced EPR signals in the teeth of volunteers who were residents in Fukushima within 80 km distance from the Fukushima Nuclear Power plant at the time of the disaster, and continued to live there for at least 3 month after the disaster. Thirty four volunteers were enrolled in this study. These measurements were made using a portable L-band EPR spectrometer, which was originally developed in the EPR Center at Dartmouth. All measurements were performed using surface loop resonators that have been specifically designed for the upper incisor teeth. Potentially these signals include not only radiation-induced signals induced by the incident but also background signals including those from prior radiation exposure from the environment and medical exposure. We demonstrated that it is feasible to transport the dosimeter to the measurement site and make valid measurements. The intensity of the signals that were obtained was not significantly above those seen in volunteers who had not had potential radiation exposures at Fukushima. PMID:27522046
W-band EPR of vanadyl complexes aggregates on the surface of Al2O3
NASA Astrophysics Data System (ADS)
Mamin, G.; Gafurov, M.; Galukhin, A.; Gracheva, I.; Murzakhanov, F.; Rodionov, A.; Orlinskii, S.
2018-05-01
Structural characterization of metalloporphyrins, asphaltenes and their aggregates in complex systems such as native hydrocarbons is in the focus of scientific and industrial interests since many years. We present W-band (95 GHz) electron paramagnetic resonance (EPR) study in the magnetic field of about 3.4 T and temperature of 100 K for Karmalinskoe oil, asphaltens and asphaltenes deposited on the surface of Al2O3. Features of the obtained spectra are described. Shift to the higher frequencies allows to separate spectrally the contributions from paramagnetic complexes of different origin and define the EPR parameters more accurately comparing to the conventional X-band (9 GHz). Changes of the EPR parameters are tracked. We suggest that the proposed approach can be used for the investigation of structure of vanadyl complexes aggregates in crude oil and their fractions.
NASA Technical Reports Server (NTRS)
Cravey, Robin L.; Tiemsin, Pacita I.
1997-01-01
This paper describes measurements which were performed on a sample of radome material in the Electromagnetic Properties Measurements Laboratory (EPML). The purpose of the measurements described in this paper was to determine the one-way transmission loss through the flat panel of radome material for a frequency range of 84 to 94 GHz, for varying incidence angles. The panel, which was manufactured by Norton Performance Plastics Corporation, was provided to the EPML by TRW. The size of the panel is 40 in x 36 in x 0.422 in and consists of a foam material with one side coated with a smooth white coating (this side will be referred to as the front side). The dielectric properties of the foam material from the inside of the panel were also determined at X-band (8.2-12.4 GHz). The W-band free space measurements are presented first, followed by the X-band dielectric properties measurements.
Hyde, James S.; Strangeway, Robert A.; Camenisch, Theodore G.; Ratke, Joseph J.; Froncisz, Wojciech
2010-01-01
This paper describes a novel experiment on nitroxide radical spin labels using a multiarm EPR W-band bridge with a loop-gap resonator (LGR). We demonstrate EPR spectroscopy of spin labels by linear sweep of the microwave frequency across the spectrum. The high bandwidth of the LGR, about 1 GHz between 3 dB points of the microwave resonance, makes this new experiment possible. A frequency-tunable yttrium iron garnet (YIG) oscillator provides sweep rates as high as 1.8 × 105 GHz/s, which corresponds to 6.3 kT/s in magnetic field-sweep units over a 44 MHz range. Two experimental domains were identified. In the first, linear frequency sweep rates were relatively slow, and pure absorption and pure dispersion spectra were obtained. This appears to be a practical mode of operation at the present level of technological development. The main advantage is the elimination of sinusoidal magnetic field modulation. In the second mode, the frequency is swept rapidly across a portion of the spectrum, and then the frequency sweep is stopped for a readout period; FID signals from a swept line oscillate at a frequency that is the difference between the spectral position of the line in frequency units and the readout position. If there is more than one line, oscillations are superimposed. The sweep rates using the YIG oscillator were too slow, and the portion of the spectrum too narrow to achieve the full EPR equivalent of Fourier transform (FT) NMR. The paper discusses technical advances required to reach this goal. The hypothesis that trapezoidal frequency sweep is an enabling technology for FT EPR is supported by this study. PMID:20462775
Misra, S K; Andronenko, S I; Tipikin, D; Freed, J H; Somani, V; Prakash, Om
2016-03-01
Detailed EPR investigations on as-grown and annealed TiO 2 nanoparticles in the anatase and rutile phases were carried out at X-band (9.6 GHz) at 77, 120-300 K and at 236 GHz at 292 K. The analysis of EPR data for as-grown and annealed anatase and rutile samples revealed the presence of several paramagnetic centers: Ti 3+ , O - , adsorbed oxygen (O 2 - ) and oxygen vacancies. On the other hand, in as-grown rutile samples, there were observed EPR lines due to adsorbed oxygen (O 2 - ) and the Fe 3+ ions in both Ti 4+ substitutional positions, with and without coupling to an oxygen vacancy in the near neighborhood. Anatase nanoparticles were completely converted to rutile phase when annealed at 1000° C, exhibiting EPR spectra similar to those exhibited by the as-grown rutile nanoparticles. The high-frequency (236 GHz) EPR data on anatase and rutile samples, recorded in the region about g = 2.0 exhibit resolved EPR lines, due to O - and O 2 - ions enabling determination of their g-values with higher precision, as well as observation of hyperfine sextets due to Mn 2+ and Mn 4+ ions in anatase.
Misra, S.K.; Andronenko, S.I.; Tipikin, D.; Freed, J. H.; Somani, V.; Prakash, Om
2016-01-01
Detailed EPR investigations on as-grown and annealed TiO2 nanoparticles in the anatase and rutile phases were carried out at X-band (9.6 GHz) at 77, 120–300 K and at 236 GHz at 292 K. The analysis of EPR data for as-grown and annealed anatase and rutile samples revealed the presence of several paramagnetic centers: Ti3+, O−, adsorbed oxygen (O2−) and oxygen vacancies. On the other hand, in as-grown rutile samples, there were observed EPR lines due to adsorbed oxygen (O2−) and the Fe3+ ions in both Ti4+ substitutional positions, with and without coupling to an oxygen vacancy in the near neighborhood. Anatase nanoparticles were completely converted to rutile phase when annealed at 1000° C, exhibiting EPR spectra similar to those exhibited by the as-grown rutile nanoparticles. The high-frequency (236 GHz) EPR data on anatase and rutile samples, recorded in the region about g = 2.0 exhibit resolved EPR lines, due to O− and O2− ions enabling determination of their g-values with higher precision, as well as observation of hyperfine sextets due to Mn2+ and Mn4+ ions in anatase. PMID:27041794
Saturation recovery EPR and ELDOR at W-band for spin labels
Froncisz, Wojciech; Camenisch, Theodore G.; Ratke, Joseph J.; Anderson, James R.; Subczynski, Witold K.; Strangeway, Robert A.; Sidabras, Jason W.; Hyde, James S.
2008-01-01
A reference-arm W-band (94 GHz) microwave bridge with two sample-irradiation arms for saturation recovery (SR) EPR and ELDOR experiments is described. Frequencies in each arm are derived from 2 GHz synthesizers that have a common time-base and are translated to 94 GHz in steps of 33 and 59 GHz. Intended applications are to nitroxide radical spin labels and spin probes in the liquid phase. An enabling technology is the use of a W-band loop-gap resonator (LGR) (J.W. Sidabras et al., Rev. Sci. Instrum. 78 (2007) 034701). The high efficiency parameter (8.2 GW−1/2 with sample) permits the saturating pump pulse level to be just 5 mW or less. Applications of SR EPR and ELDOR to the hydrophilic spin labels 3-carbamoyl-2,2,5,5-tetra-methyl-3-pyrroline-1-yloxyl (CTPO) and 2,2,6,6,-tetramethyl-4-piperidone-1-oxyl (TEMPONE) are described in detail. In the SR ELDOR experiment, nitrogen nuclear relaxation as well as Heisenberg exchange transfer saturation from pumped to observed hyperfine transitions. SR ELDOR was found to be an essential method for measurements of saturation transfer rates for small molecules such as TEMPONE. Free induction decay (FID) signals for small nitroxides at W-band are also reported. Results are compared with multifrequency measurements of T1e previously reported for these molecules in the range of 2 to 35 GHz (J.S. Hyde et al., J. Phys. Chem. B 108 (2004) 9524–9529). The values of T1e decrease at 94 GHz relative to values at 35 GHz. PMID:18547848
Möser, J; Lips, K; Tseytlin, M; Eaton, G R; Eaton, S S; Schnegg, A
2017-08-01
X-band rapid-scan EPR was implemented on a commercially available Bruker ELEXSYS E580 spectrometer. Room temperature rapid-scan and continuous-wave EPR spectra were recorded for amorphous silicon powder samples. By comparing the resulting signal intensities the feasibility of performing quantitative rapid-scan EPR is demonstrated. For different hydrogenated amorphous silicon samples, rapid-scan EPR results in signal-to-noise improvements by factors between 10 and 50. Rapid-scan EPR is thus capable of improving the detection limit of quantitative EPR by at least one order of magnitude. In addition, we provide a recipe for setting up and calibrating a conventional pulsed and continuous-wave EPR spectrometer for rapid-scan EPR. Copyright © 2017 Elsevier Inc. All rights reserved.
Dental radiography: tooth enamel EPR dose assessment from Rando phantom measurements
NASA Astrophysics Data System (ADS)
Aragno, D.; Fattibene, P.; Onori, S.; Aragno, D.; Fattibene, P.
2000-09-01
Electron paramagnetic resonance dosimetry of tooth enamel is now established as a suitable method for individual dose reconstruction following radiation accidents. The accuracy of the method is limited by some confounding factors, among which is the dose received due to medical x-ray irradiation. In the present paper the EPR response of tooth enamel to endoral examination was experimentally evaluated using an anthropomorphic phantom. The dose to enamel for a single exposure of a typical dental examination performed with a new x-ray generation unit working at 65 kVp gave rise to a CO2- signal of intensity similar to that induced by a dose of about 2 mGy of 60Co. EPR measurements were performed on the entire tooth with no attempt to separate buccal and lingual components. Also the dose to enamel for an orthopantomography exam was estimated. It was derived from TLD measurements as equivalent to 0.2 mGy of 60Co. In view of application to risk assessment analysis, in the present work the value for the ratio of the reference dose at the phantom surface measured with TLD to the dose at the tooth measured with EPR was determined.
X-ray absorption spectroscopy and EPR studies of oriented spinach thylakoid preparations
DOE Office of Scientific and Technical Information (OSTI.GOV)
Andrews, J.C.
In this study, oriented Photosystem II (PS II) particles from spinach chloroplasts are studied with electron paramagnetic resonance (EPR) and x-ray absorption spectroscopy (XAS) to determine more details of the structure of the oxygen evolving complex (OEC). The nature of halide binding to Mn is also studied with Cl K-edge and Mn EXAFS (extended x-ray absorption fine structure) of Mn-Cl model compounds, and with Mn EXAFS of oriented PS II in which Br has replaced Cl. Attention is focused on the following: photosynthesis and the oxygen evolving complex; determination of mosaic spread in oriented photosystem II particles from signal IImore » EPR measurement; oriented EXAFS--studies of PS II in the S{sub 2} state; structural changes in PS II as a result of treatment with ammonia: EPR and XAS studies; studies of halide binding to Mn: Cl K-edge and Mn EXAFS of Mn-Cl model compounds and Mn EXAFS of oriented Br-treated photosystem II.« less
In vivo and ex vivo EPR detection of spin-labelled ovalbumin in mice.
Abramović, Zrinka; Brgles, Marija; Habjanec, Lidija; Tomasić, Jelka; Sentjurc, Marjeta; Frkanec, Ruza
2010-10-01
In this study, spin-labelled ovalbumin (SL-OVA), free or entrapped in liposomes, was administered to mice subcutaneously (s.c.) or intravenously (i.v.) with the aim to determine the conditions for pharmacokinetic studies of spin-labelled proteins by EPR and to measure the time course of SL-OVA distribution in vivo in live mice and ex vivo in isolated organs. Upon s.c. administration, the decay of the EPR signal was followed for 60min at the site of application using an L-band EPR spectrometer. Within this time period, the signal of free SL-OVA was diminished by about 70%. It was estimated with the help of the oxidizing agent K(3)[(FeCN)(6)] that approximately 30% was a consequence of the spin label reduction to EPR non-visible hydroxylamine and about 40% was due to the SL-OVA elimination from the site of measurement. For liposome encapsulated SL-OVA, the intensity diminished only by approx. 40% in the same period, indicating that liposomes successfully protect the protein from reduction. EPR signal could not be detected directly over live mouse organs within 60min after s.c. application of SL-OVA. With the available L-band EPR spectrometer, the measurements at the site of s.c. application are possible if the amount of SL-OVA applied to a mouse is more than 3mg. For the pharmacokinetic studies of the protein distribution in organs after s.c. or i.v. injection the concentration of the spin-labelled protein should be more than 0.5mmol/kg. After i.v. administration, only ex vivo measurements were possible using an X-band EPR spectrometer, since the total amount of SL-OVA was not sufficient for in vivo detection and also because of rapid reduction of nitroxide. After 2min, the protein was preferentially distributed to liver and, to a smaller extent, to spleen.
NASA Astrophysics Data System (ADS)
Mainali, Laxman; Feix, Jimmy B.; Hyde, James S.; Subczynski, Witold K.
2011-10-01
There are no easily obtainable EPR spectral parameters for lipid spin labels that describe profiles of membrane fluidity. The order parameter, which is most often used as a measure of membrane fluidity, describes the amplitude of wobbling motion of alkyl chains relative to the membrane normal and does not contain explicitly time or velocity. Thus, this parameter can be considered as nondynamic. The spin-lattice relaxation rate ( T1-1) obtained from saturation-recovery EPR measurements of lipid spin labels in deoxygenated samples depends primarily on the rotational correlation time of the nitroxide moiety within the lipid bilayer. Thus, T1-1 can be used as a convenient quantitative measure of membrane fluidity that reflects local membrane dynamics. T1-1 profiles obtained for 1-palmitoyl-2-( n-doxylstearoyl)phosphatidylcholine ( n-PC) spin labels in dimyristoylphosphatidylcholine (DMPC) membranes with and without 50 mol% cholesterol are presented in parallel with profiles of the rotational diffusion coefficient, R⊥, obtained from simulation of EPR spectra using Freed's model. These profiles are compared with profiles of the order parameter obtained directly from EPR spectra and with profiles of the order parameter obtained from simulation of EPR spectra. It is shown that T1-1 and R⊥ profiles reveal changes in membrane fluidity that depend on the motional properties of the lipid alkyl chain. We find that cholesterol has a rigidifying effect only to the depth occupied by the rigid steroid ring structure and a fluidizing effect at deeper locations. These effects cannot be differentiated by profiles of the order parameter. All profiles in this study were obtained at X-band (9.5 GHz).
DSN 70-meter antenna X- and S-band calibration. Part 1: Gain measurements
NASA Technical Reports Server (NTRS)
Richter, P. H.; Slobin, S. D.
1989-01-01
Aperture efficiency measurements made during 1988 on the three 70-m stations (DSS-14, DSS-43, and DSS-63) at X-band (8420 MHz) and S-band (2295 MHz) have been analyzed and reduced to yield best estimates of antenna gain versus elevation. The analysis has been carried out by fitting the gain data to a theoretical expression based on the Ruze formula. Newly derived flux density and source-size correction factors for the natural radio calibration sources used in the measurements have been used in the reduction of the data. Peak gains measured at the three stations were 74.18 (plus or minus 0.10) dBi at X-band, and 63.34 (plus or minus 0.03) dBi at S-band, with corresponding peak aperture efficiencies of 0.687 (plus or minus 0.015) and 0.762 (plus or minus 0.006), respectively. The values quoted assume no atmosphere is present, and the estimated absolute accuracy of the gain measurements is approximately plus or minus 0.2 dB at X-band and plus or minus 0.1 dB at S-band (1-sigma values).
An 'X-banded' Tidbinbilla interferometer
NASA Technical Reports Server (NTRS)
Batty, Michael J.; Gardyne, R. G.; Gay, G. J.; Jauncy, David L.; Gulkis, S.; Kirk, A.
1986-01-01
The recent upgrading of the Tidbinbilla two-element interferometer to simultaneous S-band (2.3 GHz) and X-band (8.4 GHz) operation has provided a powerful new astronomical facility for weak radio source measurement in the Southern Hemisphere. The new X-band system has a minimum fringe spacing of 38 arcsec, and about the same positional measurement capability (approximately 2 arcsec) and sensitivity (1 s rms noise of 10 mJy) as the previous S-band system. However, the far lower confusion limit will allow detection and accurate positional measurements for sources as weak as a few millijanskys. This capability will be invaluable for observations of radio stars, X-ray sources and other weak, compact radio sources.
EPR-based distance measurements at ambient temperature.
Krumkacheva, Olesya; Bagryanskaya, Elena
2017-07-01
Pulsed dipolar (PD) EPR spectroscopy is a powerful technique allowing for distance measurements between spin labels in the range of 2.5-10.0nm. It was proposed more than 30years ago, and nowadays is widely used in biophysics and materials science. Until recently, PD EPR experiments were limited to cryogenic temperatures (T<80K). Recently, application of spin labels with long electron spin dephasing time at room temperature such as triarylmethyl radicals and nitroxides with bulky substituents at a position close to radical centers enabled measurements at room temperature and even at physiologically relevant temperatures by PD EPR as well as other approaches based on EPR (e.g., relaxation enhancement; RE). In this paper, we review the features of PD EPR and RE at ambient temperatures, in particular, requirements on electron spin phase memory time, ways of immobilization of biomolecules, the influence of a linker between the spin probe and biomolecule, and future opportunities. Copyright © 2017 Elsevier Inc. All rights reserved.
Mapping Local Protein Electrostatics by EPR of pH-Sensitive Thiol-Specific Nitroxide† ¶
Voinov, Maxim A.; Ruuge, Andres; Reznikov, Vladimir A.; Grigor’ev, Igor A.; Smirnov, Alex I.
2013-01-01
A first thiol-specific pH-sensitive nitroxide spin label of the imidazolidine series -methanethiosulfonic acid S-(1-oxyl-2,2,3,5,5-pentamethylimidazolidin-4-ylmethyl) ester (IMTSL) - has been synthesized and characterized. X- (9 GHz) and W-band (94 GHz) EPR spectral parameters of the new spin label in its free form and covalently attached to an amino acid cysteine and a tripeptide glutathione were studied as a function of pH and solvent polarity. pKa value of protonatable tertiary amino group of the spin label was found to be unaffected by other ionizable groups present in side chains of unstructured small peptides. The W-band EPR spectra were shown to allow for pKa determination from precise g-factor measurements. Is has been demonstrated that high accuracy of pKa determination for pH-sensitive nitroxides could be achieved regardless the frequency of measurements or the regime of spin exchange: fast at X-band and slow at W-band. IMTSL was found to react specifically with a model protein - iso-1-cytochrome c from yeast Saccharomyces cerevisiae - giving EPR spectra very similar to those of the most commonly employed cysteine-specific label MTSL. CD data indicated no perturbations to the overall protein structure upon IMTSL labeling. It was found that for IMTSL, giso correlates linearly with Aiso but the slopes are different for the neutral and charged forms of the nitroxide. This finding was attributed to the solvent effects on the spin density at the oxygen atom of the N–O group and on the excitation energy of the oxygen lone-pair orbital. PMID:18426227
EPR and photoluminescence study of irradiated anion-defective alumina single crystals
NASA Astrophysics Data System (ADS)
Kortov, V. S.; Ananchenko, D. V.; Konev, S. F.; Pustovarov, V. A.
2017-09-01
Electron paramagnetic resonance (EPR) and photoluminescence (PL) spectra of anion-defective alumina single crystals were measured. Exposure to a dose 10 Gy-1 kGy causes isotropic EPR signal of a complex form, this signal contains narrow and broad components. At the same time, in the PL spectrum alongside with a band of F+-centers (3.8 eV) an additional emission band with the maximum of 2.25 eV is registered. This band corresponds to aggregate F22+-centers which were create under irradiation. By comparing measurements in EPR and PL spectra with further stepped annealing in the temperature range of 773-1473 K of the samples exposed to the same doses, we were able to conclude that a narrow component of isotropic EPR signal is associated with the formation of paramagnetic F22+-centers under irradiation. A wide component can be caused by deep hole traps which are created by a complex defect (VAl2- - F+) with a localized hole.
C (G)-Band & X (I) - Band Noncoherent Radar Transponder Performance Specification Standard
2002-04-01
TRAINING RANGE NEVADA TEST SITE STANDARD 262-02 ELECTRONIC TRAJECTORY MEASUREMENTS GROUP C (G) – BAND & X (I) – BAND NONCOHERENT RADAR...Date 00 Apr 2002 Report Type N/A Dates Covered (from... to) - Title and Subtitle C (G)-Band & X (I) - Band Noncoherent Radar Transponder...Number of Pages 157 i STANDARD 262-02 C (G) – BAND & X (I) – BAND NONCOHERENT RADAR TRANSPONDER PERFORMANCE SPECIFICATION STANDARD APRIL 2002 Prepared by
Consentius, Philipp; Gohlke, Ulrich; Loll, Bernhard; Alings, Claudia; Heinemann, Udo; Wahl, Markus C; Risse, Thomas
2017-08-09
Electron paramagnetic resonance (EPR) spectroscopy in combination with site-directed spin labeling is used to investigate the structure and dynamics of conformationally constrained spin labels in T4 lysozyme single crystals. Within a single crystal, the oriented ensemble of spin bearing moieties results in a strong angle dependence of the EPR spectra. A quantitative description of the EPR spectra requires the determination of the unit cell orientation with respect to the sample tube and the orientation of the spin bearing moieties within the crystal lattice. Angle dependent EPR spectra were analyzed by line shape simulations using the stochastic Liouville equation approach developed by Freed and co-workers and an effective Hamiltonian approach. The gain in spectral information obtained from the EPR spectra of single crystalline samples taken at different frequencies, namely the X-band and Q-band, allows us to discriminate between motional models describing the spectra of isotropic solutions similarly well. In addition, it is shown that the angle dependent single crystal spectra allow us to identify two spin label rotamers with very similar side chain dynamics. These results demonstrate the utility of single crystal EPR spectroscopy in combination with spectral line shape simulation techniques to extract valuable dynamic information not readily available from the analysis of isotropic systems. In addition, it will be shown that the loss of electron density in high resolution diffraction experiments at room temperature does not allow us to conclude that there is significant structural disorder in the system.
X-Band Rapid-Scan Electron Paramagnetic Resonance of Radiation-Induced Defects in Tooth Enamel
Yu, Zhelin; Romanyukha, Alexander; Eaton, Sandra S.; Eaton, Gareth R.
2015-01-01
X-band rapid-scan electron paramagnetic resonance (EPR) spectra from tooth enamel samples irradiated with doses of 0.5, 1 and 10 Gy had substantially improved signal-to-noise relative to conventional continuous wave EPR. The radiation-induced signal in 60 mg of a tooth enamel sample irradiated with a 0.5 Gy dose was readily characterized in spectra recorded with 34 min data acquisition times. The coefficient of variance of the calculated dose for a 1 Gy irradiated sample, based on simulation of the first-derivative spectra for three replicates as the sum of native and radiation-induced signals, was 3.9% for continuous wave and 0.4% for rapid scan. PMID:26207683
A sub-Kelvin cryogen-free EPR system.
Melhuish, Simon J; Stott, Chloe; Ariciu, Ana-Maria; Martinis, Lorenzo; McCulloch, Mark; Piccirillo, Lucio; Collison, David; Tuna, Floriana; Winpenny, Richard
2017-09-01
We present an EPR instrument built for operation at Q band below 1K. Our cryogen-free Dewar integrates with a commercial electro-magnet and bridge. A description of the cryogenic and RF systems is given, along with the adaptations to the standard EPR experiment for operation at sub-Kelvin temperatures. As a first experiment, the EPR spectra of powdered Cr 12 O 9 (OH) 3 [Formula: see text] were measured. The sub-Kelvin EPR spectra agree well with predictions, and the performance of the sub-Kelvin system at 5K is compared to that of a commercial spectrometer. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.
NASA Astrophysics Data System (ADS)
Yu, Michelle A.; Egawa, Tsuyoshi; Yeh, Syun-Ru; Rousseau, Denis L.; Gerfen, Gary J.
2010-04-01
The reaction intermediates of reduced bovine Cytochrome c Oxidase (CcO) were trapped following its reaction with oxygen at 50 μs-6 ms by innovative freeze-quenching methods and studied by EPR. When the enzyme was reduced with either ascorbate or dithionite, distinct radicals were generated; X-band (9 GHz) and D-band (130 GHz) CW-EPR measurements support the assignments of these radicals to ascorbyl and sulfur dioxide anion radical (SO2-rad), respectively. The X-band spectra show a linewidth of 12 G for the ascorbyl radical and 11 G for the SO2-rad radical and an isotropic g-value of 2.005 for both species. The D-band spectra reveal clear distinctions in the g-tensors and powder patterns of the two species. The ascorbyl radical spectrum displays approximate axial symmetry with g-values of gx = 2.0068, gy = 2.0066, and gz = 2.0023. The SO2-rad>/SUP> radical has rhombic symmetry with g-values of gx = 2.0089, gy = 2.0052, and gz = 2.0017. When the contributions from the ascorbyl and SO2-rad radicals were removed, no protein-based radical on CcO could be identified in the EPR spectra.
X-band Uplink Ground Systems Development
NASA Technical Reports Server (NTRS)
Johns, C. E.
1984-01-01
The development of the X-band exciter and Doppler extractor equipment for the X-band uplink was completed. Stability measurements were made on the exciter and Doppler reference signals and the results are presented.
Measurements and Simulations of Nadir-Viewing Radar Returns from the Melting Layer at X- and W-Bands
NASA Technical Reports Server (NTRS)
Liao, Liang; Meneghini, Robert; Tian, Lin; Heymsfield, Gerald M.
2010-01-01
Simulated radar signatures within the melting layer in stratiform rain, namely the radar bright band, are checked by means of comparisons with simultaneous measurements of the bright band made by the EDOP (X-band) and CRS (W-band) airborne Doppler radars during the CRYSTAL-FACE campaign in 2002. A stratified-sphere model, allowing the fractional water content to vary along the radius of the particle, is used to compute the scattering properties of individual melting snowflakes. Using the effective dielectric constants computed by the conjugate gradient-fast Fourier transform (CGFFT) numerical method for X and W bands, and expressing the fractional water content of melting particle as an exponential function in particle radius, it is found that at X band the simulated radar bright-band profiles are in an excellent agreement with the measured profiles. It is also found that the simulated W-band profiles usually resemble the shapes of the measured bright-band profiles even though persistent offsets between them are present. These offsets, however, can be explained by the attenuation caused by cloud water and water vapor at W band. This is confirmed by the comparisons of the radar profiles made in the rain regions where the un-attenuated W-band reflectivity profiles can be estimated through the X- and W band Doppler velocity measurements. The bright-band model described in this paper has the potential to be used effectively for both radar and radiometer algorithms relevant to the TRMM and GPM satellite missions.
Optical and EPR studies of barium alumino borate glasses containing Cu2+ ions
NASA Astrophysics Data System (ADS)
Ahmed, Mohamad Raheem; Phani, A. V. Lalitha; Narsimha Chary, M.; Shareefuddin, Md.
2018-05-01
Glass containing Cu2+ ions in (30-x) BaO-xAl2O3-69.5B2O3-0.5CuO (0 ≤ x ≤ 15 mol %) were prepared by the conventional melt quenching technique. Peak free X-ray diffractograms confirmed the amorphous nature of the glass samples. Spectroscopic studies such as optical absorption, EPR were studied to understand the effect of modifier oxide and CuO dopant. From EPR spectra the spin-Hamiltonian parameter were evaluated. The ground state of Cu2+ is dx2-y2 (2B1g state) and the site symmetry around Cu2+ is tetragonally distorted octahedral. A broad optical absorption band was observed for all the glasses containing Cu2+ ions corresponding to the 2B1g → 2B2g transition. The optical band gap and Urbach energy values are calculated.
Yokoyama, Hidekatsu
2012-01-01
Direct irradiation of a sample using a quartz oscillator operating at 250 MHz was performed for EPR measurements. Because a quartz oscillator is a frequency fixed oscillator, the operating frequency of an EPR resonator (loop-gap type) was tuned to that of the quartz oscillator by using a single-turn coil with a varactor diode attached (frequency shift coil). Because the frequency shift coil was mobile, the distance between the EPR resonator and the coil could be changed. Coarse control of the resonant frequency was achieved by changing this distance mechanically, while fine frequency control was implemented by changing the capacitance of the varactor electrically. In this condition, EPR measurements of a phantom (comprised of agar with a nitroxide radical and physiological saline solution) were made. To compare the presented method with a conventional method, the EPR measurements were also done by using a synthesizer at the same EPR frequency. In the conventional method, the noise level increased at high irradiation power. Because such an increase in the noise was not observed in the presented method, high sensitivity was obtained at high irradiation power. Copyright © 2011 Elsevier Inc. All rights reserved.
Relativistic Nonlocality and the EPR Paradox
NASA Astrophysics Data System (ADS)
Chamberlain, Thomas
2014-03-01
The exact violation of Bell's Inequalities is obtained with a local realistic model for spin. The model treats one particle that comprises a quantum ensemble and simulates the EPR data one coincidence at a time as a product state. Such a spin is represented by operators σx , iσy ,σz in its body frame rather than the usual set of σX ,σY ,σZ in the laboratory frame. This model, assumed valid in the absence of a measuring probe, contains both quantum polarizations and coherences. Each carries half the EPR correlation, but only half can be measured using coincidence techniques. The model further predicts the filter angles that maximize the spin correlation in EPR experiments.
Ivannikov, Alexander I; Khailov, Artem M; Orlenko, Sergey P; Skvortsov, Valeri G; Stepanenko, Valeri F; Zhumadilov, Kassym Sh; Williams, Benjamin B; Flood, Ann B; Swartz, Harold M
2016-12-01
The aim of the study is to determine the average intensity and variation of the native background signal amplitude (NSA) and of the solar light-induced signal amplitude (LSA) in electron paramagnetic resonance (EPR) spectra of tooth enamel for different kinds of teeth and different groups of people. These values are necessary for determination of the intensity of the radiation-induced signal amplitude (RSA) by subtraction of the expected NSA and LSA from the total signal amplitude measured in L-band for in vivo EPR dosimetry. Variation of these signals should be taken into account when estimating the uncertainty of the estimated RSA. A new analysis of several hundred EPR spectra that were measured earlier at X-band in a large-scale examination of the population of the Central Russia was performed. Based on this analysis, the average values and the variation (standard deviation, SD) of the amplitude of the NSA for the teeth from different positions, as well as LSA in outer enamel of the front teeth for different population groups, were determined. To convert data acquired at X-band to values corresponding to the conditions of measurement at L-band, the experimental dependencies of the intensities of the RSA, LSA and NSA on the m.w. power, measured at both X and L-band, were analysed. For the two central upper incisors, which are mainly used in in vivo dosimetry, the mean LSA annual rate induced only in the outer side enamel and its variation were obtained as 10 ± 2 (SD = 8) mGy y -1 , the same for X- and L-bands (results are presented as the mean ± error of mean). Mean NSA in enamel and its variation for the upper incisors was calculated at 2.0 ± 0.2 (SD = 0.5) Gy, relative to the calibrated RSA dose-response to gamma radiation measured under non-power saturation conditions at X-band. Assuming the same value for L-band under non-power saturating conditions, then for in vivo measurements at L-band at 25 mW (power saturation conditions), a mean NSA and its
Ivannikov, Alexander I.; Khailov, Artem M.; Orlenko, Sergey P.; Skvortsov, Valeri G.; Stepanenko, Valeri F.; Zhumadilov, Kassym Sh.; Williams, Benjamin B.; Flood, Ann B.; Swartz, Harold M.
2016-01-01
The aim of the study is to determine the average intensity and variation of the native background signal amplitude (NSA) and of the solar light-induced signal amplitude (LSA) in electron paramagnetic resonance (EPR) spectra of tooth enamel for different kinds of teeth and different groups of people. These values are necessary for determination of the intensity of the radiation-induced signal amplitude (RSA) by subtraction of the expected NSA and LSA from the total signal amplitude measured in L-band for in vivo EPR dosimetry. Variation of these signals should be taken into account when estimating the uncertainty of the estimated RSA. A new analysis of several hundred EPR spectra that were measured earlier at X-band in a large-scale examination of the population of the Central Russia was performed. Based on this analysis, the average values and the variation (standard deviation, SD) of the amplitude of the NSA for the teeth from different positions, as well as LSA in outer enamel of the front teeth for different population groups, were determined. To convert data acquired at X-band to values corresponding to the conditions of measurement at L-band, the experimental dependencies of the intensities of the RSA, LSA and NSA on the m.w. power, measured at both X and L-band, were analysed. For the two central upper incisors, which are mainly used in in vivo dosimetry, the mean LSA annual rate induced only in the outer side enamel and its variation were obtained as 10 ± 2 (SD = 8) mGy y−1, the same for X- and L-bands (results are presented as the mean ± error of mean). Mean NSA in enamel and its variation for the upper incisors was calculated at 2.0 ± 0.2 (SD = 0.5) Gy, relative to the calibrated RSA dose–response to gamma radiation measured under non-power saturation conditions at X-band. Assuming the same value for L-band under non-power saturating conditions, then for in vivo measurements at L-band at 25 mW (power saturation conditions), a mean NSA and
ENDOR-Induced EPR of Disordered Systems: Application to X-Irradiated Alanine.
Kusakovskij, Jevgenij; Maes, Kwinten; Callens, Freddy; Vrielinck, Henk
2018-02-15
The electron paramagnetic resonance (EPR) spectra of radiation-induced radicals in organic solids are generally composed of multiple components that largely overlap due to their similar weak g anisotropy and a large number of hyperfine (HF) interactions. Such properties make these systems difficult to study using standard cw EPR spectroscopy even in single crystals. Electron-nuclear double-resonance (ENDOR) spectroscopy is a powerful and widely used complementary technique. In particular, ENDOR-induced EPR (EIE) experiments are useful for separating the overlapping contributions. In the present work, these techniques were employed to study the EPR spectrum of stable radicals in X-irradiated alanine, which is widely used in dosimetric applications. The principal values of all major proton HF interactions of the dominant radicals were determined by analyzing the magnetic field dependence of the ENDOR spectrum at 50 K, where the rotation of methyl groups is frozen. Accurate simulations of the EPR spectrum were performed after the major components were separated using an EIE analysis. As a result, new evidence in favor of the model of the second dominant radical was obtained.
Broadband Transmission EPR Spectroscopy
Hagen, Wilfred R.
2013-01-01
EPR spectroscopy employs a resonator operating at a single microwave frequency and phase-sensitive detection using modulation of the magnetic field. The X-band spectrometer is the general standard with a frequency in the 9–10 GHz range. Most (bio)molecular EPR spectra are determined by a combination of the frequency-dependent electronic Zeeman interaction and a number of frequency-independent interactions, notably, electron spin – nuclear spin interactions and electron spin – electron spin interactions, and unambiguous analysis requires data collection at different frequencies. Extant and long-standing practice is to use a different spectrometer for each frequency. We explore the alternative of replacing the narrow-band source plus single-mode resonator with a continuously tunable microwave source plus a non-resonant coaxial transmission cell in an unmodulated external field. Our source is an arbitrary wave digital signal generator producing an amplitude-modulated sinusoidal microwave in combination with a broadband amplifier for 0.8–2.7 GHz. Theory is developed for coaxial transmission with EPR detection as a function of cell dimensions and materials. We explore examples of a doublet system, a high-spin system, and an integer-spin system. Long, straigth, helical, and helico-toroidal cells are developed and tested with dilute aqueous solutions of spin label hydroxy-tempo. A detection limit of circa 5 µM HO-tempo in water at 800 MHz is obtained for the present setup, and possibilities for future improvement are discussed. PMID:23555819
Wright, John J; Salvadori, Enrico; Bridges, Hannah R; Hirst, Judy; Roessler, Maxie M
2016-09-01
EPR-based potentiometric titrations are a well-established method for determining the reduction potentials of cofactors in large and complex proteins with at least one EPR-active state. However, such titrations require large amounts of protein. Here, we report a new method that requires an order of magnitude less protein than previously described methods, and that provides EPR samples suitable for measurements at both X- and Q-band microwave frequencies. We demonstrate our method by determining the reduction potential of the terminal [4Fe-4S] cluster (N2) in the intramolecular electron-transfer relay in mammalian respiratory complex I. The value determined by our method, E m7 =-158mV, is precise, reproducible, and consistent with previously reported values. Our small-volume potentiometric titration method will facilitate detailed investigations of EPR-active centres in non-abundant and refractory proteins that can only be prepared in small quantities. Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.
Exciter For X-Band Transmitter And Receiver
NASA Technical Reports Server (NTRS)
Johns, Carl E.
1989-01-01
Report describes developmental X-band exciter for X-band uplink subsystem of Deep Space Network. X-band transmitter-exciting signal expected to have fractional frequency stability of 5.2 X 10 to negative 15th power during 1,000-second integration period. Generates coherent test signals for S- and X-band Block III translator of Deep Space Network, Doppler-reference signal for associated Doppler-extractor system, first-local-oscillator signal for associated receiver, and reference signal for associated ranging subsystem. Tests of prototype exciter show controlling and monitoring and internal phase-correcting loops perform according to applicable design criteria. Measurements of stability of frequency and of single-sideband noise spectral density of transmitter-exciting signal made subsequently.
Mariner Venus Mercury 1973 S/X-band experiment
NASA Technical Reports Server (NTRS)
Levy, G. S.
1977-01-01
The S/X-band experiment on the Mariner Venus/Mercury 1973 spacecraft constituted a unique opportunity to demonstrate the capability of an X-band downlink coherent with the normal S-band downlink. This was both a technological and scientific experiment, and the results indicated that it was successful in both cases. Analysis of the tracking data shows that the new S/X data type was capable of reducing the miss distance at the planet Mercury by 80% (post-processed data). The use of S/X electron content was demonstrated by comparison with Faraday rotation data. An X-band turnaround telemetry experiment showed the feasibility of a planetary X-band link. In the science area, the model atmospheric environment of Venus was refined. The ionosphere of the planet was measured to a higher accuracy than before, and the value of the dual-frequency link for measuring the scale size of turbulence was demonstrated. The estimate of the scale size was increased from 100 m to above 5 km.
Toward 2D and 3D imaging of magnetic nanoparticles using EPR measurements.
Coene, A; Crevecoeur, G; Leliaert, J; Dupré, L
2015-09-01
Magnetic nanoparticles (MNPs) are an important asset in many biomedical applications. An effective working of these applications requires an accurate knowledge of the spatial MNP distribution. A promising, noninvasive, and sensitive technique to visualize MNP distributions in vivo is electron paramagnetic resonance (EPR). Currently only 1D MNP distributions can be reconstructed. In this paper, the authors propose extending 1D EPR toward 2D and 3D using computer simulations to allow accurate imaging of MNP distributions. To find the MNP distribution belonging to EPR measurements, an inverse problem needs to be solved. The solution of this inverse problem highly depends on the stability of the inverse problem. The authors adapt 1D EPR imaging to realize the imaging of multidimensional MNP distributions. Furthermore, the authors introduce partial volume excitation in which only parts of the volume are imaged to increase stability of the inverse solution and to speed up the measurements. The authors simulate EPR measurements of different 2D and 3D MNP distributions and solve the inverse problem. The stability is evaluated by calculating the condition measure and by comparing the actual MNP distribution to the reconstructed MNP distribution. Based on these simulations, the authors define requirements for the EPR system to cope with the added dimensions. Moreover, the authors investigate how EPR measurements should be conducted to improve the stability of the associated inverse problem and to increase reconstruction quality. The approach used in 1D EPR can only be employed for the reconstruction of small volumes in 2D and 3D EPRs due to numerical instability of the inverse solution. The authors performed EPR measurements of increasing cylindrical volumes and evaluated the condition measure. This showed that a reduction of the inherent symmetry in the EPR methodology is necessary. By reducing the symmetry of the EPR setup, quantitative images of larger volumes can be
X-band uplink ground systems development: Part 2
NASA Technical Reports Server (NTRS)
Johns, C. E.
1987-01-01
The prototype X-band exciter testing has been completed. Stability and single-sideband phase noise measurements have been made on the X-band exciter signal (7.145-7.235 GHz) and on the coherent X- and S-band receiver test signals (8.4-8.5 GHz and 2.29-2.3 GHz) generated within the exciter equipment. Outputs are well within error budgets.
Investigating Pigment Radicals in Black Rice Using HPLC and Multi-EPR.
Nakagawa, Kouichi; Maeda, Hayato
2017-01-01
We investigated the location and distribution of paramagnetic species in black and white rice using electron paramagnetic resonance (EPR), X-band (9 GHz) EPR imaging (EPRI), and HPLC. EPR primarily detected two paramagnetic species in black rice, which were identified as a stable radical and Mn 2+ species, based on the g values and hyperfine components of the EPR signals. The signal from the stable radical appeared at g ≈ 2.00 and was relatively strong and stable. Subsequent noninvasive two-dimensional (2D) EPRI revealed that this stable radical was primarily located in the pigmented region of black rice, while very few radicals were observed in the rice interior. Pigments extracted from black rice were analyzed using HPLC; the major compound was found to be cyanidin-3-glucoside. EPR and HPLC results indicate that the stable radical was only found within the pigmented region of the rice, and that it could either be cyanidin-3-glucoside, or one of its oxidative decomposition products.
A Local Realistic Reconciliation of the EPR Paradox
NASA Astrophysics Data System (ADS)
Sanctuary, Bryan
2014-03-01
The exact violation of Bell's Inequalities is obtained with a local realistic model for spin. The model treats one particle that comprises a quantum ensemble and simulates the EPR data one coincidence at a time as a product state. Such a spin is represented by operators σx , iσy ,σz in its body frame rather than the usual set of σX ,σY ,σZ in the laboratory frame. This model, assumed valid in the absence of a measuring probe, contains both quantum polarizations and coherences. Each carries half the EPR correlation, but only half can be measured using coincidence techniques. The model further predicts the filter angles that maximize the spin correlation in EPR experiments.
Simulation of radar backscattering from snowpack at X-band and Ku-band
NASA Astrophysics Data System (ADS)
Gay, Michel; Phan, Xuan-Vu; Ferro-Famil, Laurent
2016-04-01
This paper presents a multilayer snowpack electromagnetic backscattering model, based on Dense Media Radiative Transfer (DMRT). This model is capable of simulating the interaction of electromagnetic wave (EMW) at X-band and Ku-band frequencies with multilayer snowpack. The air-snow interface and snow-ground backscattering components are calculated using the Integral Equation Model (IEM) by [1], whereas the volume backscattering component is calculated based on the solution of Vector Radiative Transfer (VRT) equation at order 1. Case study has been carried out using measurement data from NoSREx project [2], which include SnowScat data in X-band and Ku-band, TerraSAR-X acquisitions and snowpack stratigraphic in-situ measurements. The results of model simulations show good agreement with the radar observations, and therefore allow the DMRT model to be used in various applications, such as data assimilation [3]. [1] A.K. Fung and K.S. Chen, "An update on the iem surface backscattering model," Geoscience and Remote Sensing Letters, IEEE, vol. 1, no. 2, pp. 75 - 77, april 2004. [2] J. Lemmetyinen, A. Kontu, J. Pulliainen, A. Wiesmann, C. Werner, T. Nagler, H. Rott, and M. Heidinger, "Technical assistance for the deployment of an x- to ku-band scatterometer during the nosrex ii experiment," Final Report, ESA ESTEC Contract No. 22671/09/NL/JA., 2011. [3] X. V. Phan, L. Ferro-Famil, M. Gay, Y. Durand, M. Dumont, S. Morin, S. Allain, G. D'Urso, and A. Girard, "3d-var multilayer assimilation of x-band sar data into a detailed snowpack model," The Cryosphere Discussions, vol. 7, no. 5, pp. 4881-4912, 2013.
Kalapsazova, M; Ivanova, S; Kukeva, R; Simova, S; Wegner, S; Zhecheva, E; Stoyanova, R
2017-10-11
Knowledge on the formation of mixed transition metal layers on lithium and sodium transition metal oxides, Li/Na(Co,Ni,Mn,)O 2 , determines the ability to control their electrochemical properties as electrode materials in alkaline ion batteries. Taking this into account, herein we combine the EPR and 23 Na MAS NMR spectroscopic techniques to gain insights into the structural peculiarities of the mixed cobalt-nickel-manganese layers of Na y Co 1-2x Ni x Mn x O 2 with a three-layer stacking (P3-type) structure. Two types of compositions are examined where diamagnetic Co 3+ and paramagnetic Ni 3+ and Mn 4+ are stabilized: Na 2/3 Co 1/3 Ni 1/3 Mn 1/3 O 2 and Na 1/2 Ni 1/2 Mn 1/2 O 2 . EPR spectroscopy operating in the X- and Q-band region is applied with an aim to improve the spectra resolution and, on the other hand, to provide straightforward information on the coordination of the transition metal ions inside the layers. The analysis of EPR spectra is based on the reference for the Mn 4+ and Ni 2+ ions occurring simultaneously in oxides with two layer stacking, P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 . Complementary to EPR, 23 Na MAS NMR spectroscopy at high spinning rates is undertaken to assess the local structure of the Na nucleus in the layered P3-Na y Co 1-2x Ni x Mn x O 2 oxides. All results are discussed taking into account the EPR and NMR data for the well-known lithium analogues O3-LiCo 1/3 Ni 1/3 Mn 1/3 O 2 and O3-LiNi 1/2 Mn 1/2 O 2 . Finally, the structure peculiarities of the transition metal layers extracted from the EPR and NMR methods are demonstrated by electrochemical intercalation of Li + ions into P3-Na y Co 1-2x Ni x Mn x O 2 .
EFFECT OF CADMIUM(II) ON FREE RADICALS IN DOPA-MELANIN TESTED BY EPR SPECTROSCOPY.
Zdybel, Magdalena; Pilawa, Barbara; Chodurek, Ewa
2015-01-01
Electron paramagnetic resonance (EPR) spectroscopy may be applied to examine interactions of melanin with metal ions and drugs. In this work EPR method was used to examination of changes in free radical system of DOPA-melanin--the model eumelanin after complexing with diamagnetic cadmium(II) ions. Cadmium(II) may affect free radicals in melanin and drugs binding by this polymer, so the knowledge of modification of properties and free radical concentration in melanin is important to pharmacy. The effect of cadmium(II) in different concentrations on free radicals in DOPA-melanin was determined. EPR spectra of DOPA-melanin, and DOPA-melanin complexes with cadmium(II) were measured by an X-band (9.3 GHz) EPR spectrometer produced by Radiopan (Poznań, Poland) and the Rapid Scan Unit from Jagmar (Krak6w, Poland). The DOPA (3,4-dihydroxyphenylalanine) to metal ions molar ratios in the reaction mixtures were 2:1, 1:1, and 1: 2. High concentrations of o-semiquinone (g ~2.0040) free radicals (~10(21)-10(22) spin/g) characterize DOPA-melanin and its complexes with cadmium(II). Formation of melanin complexes with cadmium(II) increase free radical concentration in DOPA-melanin. The highest free radical concentration was obtained for DOPA-melanin-cadmium(II) (1:1) complexes. Broad EPR lines with linewidths: 0.37-0.73 mT, were measured. Linewidths increase after binding of cadmium(II) to melanin. Changes of integral intensities and linewidths with increasing microwave power indicate the homogeneous broadening of EPR lines, independently on the metal ion concentration. Slow spin-lattice relaxation processes existed in all the tested samples, their EPR lines saturated at low microwave powers. Cadmium(II) causes fastening of spin-lattice relaxation processes in DOPA-melanin. The EPR results bring to light the effect of cadmium(II) on free radicals in melanin, and probably as the consequence on drug binding to eumelanin.
Microwave (EPR) measurements of the penetration depth measurements of high-Tc superconductors
NASA Technical Reports Server (NTRS)
Dalal, N. S.; Rakvin, B.; Mahl, T. A.; Bhalla, A. S.; Sheng, Z. Z.
1991-01-01
The use is discussed of electron paramagnetic resonance (EPR) as a quick and easily accessible method for measuring the London penetration depth, lambda for the high T sub c superconductors. The method uses the broadening of the EPR signal, due to the emergence of the magnetic flux lattice, of a free radical adsorbed on the surface of the sample. The second moment, of the EPR signal below T sub c is fitted to the Brandt equation for a simple triangular lattice. The precision of this method compares quite favorably with those of the more standard methods such as micro sup(+)SR, neutron scattering, and magnetic susceptibility.
NASA Astrophysics Data System (ADS)
Johansson, A. M.; King, J. A.; Doulgeris, A. P.; Gerland, S.; Singha, S.; Spreen, G.; Busche, T.
2017-01-01
In this study, we compare colocated near-coincident X-, C-, and L-band fully polarimetry SAR satellite images with helicopter-borne ice thickness measurements acquired during the Norwegian Young sea ICE 2015 (N-ICE2015) expedition in the region of the Arctic Ocean north of Svalbard in April 2015. The air-borne surveys provide near-coincident snow plus ice thickness, surface roughness data, and photographs. This unique data set allows us to investigate how the different frequencies can complement one another for sea ice studies, but also to raise awareness of limitations. X-band and L-band satellite scenes were shown to be a useful complement to the standard SAR frequency for sea ice monitoring (C-band) for lead ice and newly formed sea ice identification. This may be in part be due to the frequency but also the high spatial resolution of these sensors. We found a relatively low correlation between snow plus ice thickness and surface roughness. Therefore, in our dataset ice thickness cannot directly be observed by SAR which has important implications for operational ice charting based on automatic segmentation.
NASA Astrophysics Data System (ADS)
Thurnauer, Marion C.; Brown, James W.; Gast, P.; Feezel, Laura L.
Suggestions that the electron acceptor, A 1, in Photosystem I is a quinone have come from both optical and epr experiments. Vitamin K 1 (phylloquinone) is present in the PSI complex with a stoichiometry of two molecules per reaction center. In order to determine if A 1 can be identified with vitamin K 1, X-band and Q-band epr properties of the vitamin K 1 radical anion in frozen alcohol solutions are examined. The results are compared to the epr properties that have been observed for the reduced A 1 acceptor in vivo. The g-values obtained for the vitamin K 1 radical anion are consistent with identifying A 1 with vitamin K 1.
NASA Astrophysics Data System (ADS)
Srinivas, B.; Hameed, Abdul; Vijaya Kumar, R.; Narasimha Chary, M.; Shareefuddin, Md.
2018-06-01
The effect of the spin probe VO2+ in 15BaO-15TeO2-10TiO2-(60-x) B2O3-xV2O5 (x = 0.2, 0.4, 0.6, 0.8 mol %) glasses has been studied by employing Electron Paramagnetic Resonance (EPR) and optical absorption spectroscopic techniques. The observed EPR spectra of VO2+ ions were attributed on the basis of well-known spin-Hamiltonian of C4V symmetry. The simulated EPR spectra for VO2+ ions in the present glass system were drawn using Easy spin software. Both the experimental and simulated spectra were found to be in good agreement with each other. The optical absorption spectra exhibited three d-d transition bands due to crystal and tetragonal fields of VO2+ ions. These bands were assigned to 2B2g→ 2Eg, 2B2g→ 2B1g and 2B2g→ 2A1g transitions. The crystal field parameters Dq, Ds and Dt values are calculated. From the EPR and optical data, the molecular bonding coefficients were evaluated. Employing the higher order perturbation formulae of the g factors for 3d1 ion under tetragonally compressed octahedral fields, theoretical studies were carried out. The spin-Hamiltonian parameters ? and ? obtained from both the experimental and theoretical methods were in good agreement with each other.
Beam Measurement of 11.424 GHz X-Band Linac for Compton Scattering X-ray Source
NASA Astrophysics Data System (ADS)
Natsui, Takuya; Mori, Azusa; Masuda, Hirotoshi; Uesaka, Mitsuru; Sakamoto, Fumito
2010-11-01
An inverse Compton scattering X-ray source for medical applications, consisting of an X-band (11.424 GHz) linac and Q-switched Nd:YAG laser, is currently being developed at the University of Tokyo. This system uses an X-band 3.5-cell thermionic cathode RF gun for electron beam generation. We can obtain a multi-bunch electron beam with this gun. The beam is accelerated to 30 MeV by a traveling-wave accelerating tube. So far, we have verified stable beam generation (around 2.3 MeV) by using the newly designed RF gun and we have succeeded in beam transportation to a beam dump.
An X-Band Gun Test Area at SLAC
DOE Office of Scientific and Technical Information (OSTI.GOV)
Limborg-Deprey, C.; Adolphsen, C.; Chu, T.S.
The X-Band Test Area (XTA) is being assembled in the NLCTA tunnel at SLAC to serve as a test facility for new RF guns. The first gun to be tested will be an upgraded version of the 5.6 cell, 200 MV/m peak field X-band gun designed at SLAC in 2003 for the Compton Scattering experiment run in ASTA. This new version includes some features implemented in 2006 on the LCLS gun such as racetrack couplers, increased mode separation and elliptical irises. These upgrades were developed in collaboration with LLNL since the same gun will be used in an injector formore » a LLNL Gamma-ray Source. Our beamline includes an X-band acceleration section which takes the electron beam up to 100 MeV and an electron beam measurement station. Other X-Band guns such as the UCLA Hybrid gun will be characterized at our facility.« less
UV EFFECTS IN TOOTH ENAMEL AND THEIR POSSIBLE APPLICATION IN EPR DOSIMETRY WITH FRONT TEETH
Sholom, S.; Desrosiers, M.; Chumak, V.; Luckyanov, N.; Simon, S.L.; Bouville, A.
2009-01-01
The effects of ultraviolet (UV) radiation on ionizing radiation biodosimetry were studied in human tooth enamel samples using the technique of electron paramagnetic resonance (EPR) in X-band. For samples in the form of grains, UV-specific EPR spectra were spectrally distinct from that produced by exposure to gamma radiation. From larger enamel samples, the UV penetration depth was determined to be in the 60–120 μm range. The difference in EPR spectra from UV exposure and from exposure to gamma radiation samples was found to be a useful marker of UV equivalent dose (defined as the apparent contribution to the gamma dose in mGy that results from UV radiation absorption) in tooth enamel. This concept was preliminarily tested on front teeth from inhabitants of the region of the Semipalatinsk Nuclear Test Site (Kazakhstan) who might have received some exposure to gamma radiation from the nuclear tests conducted there as well as from normal UV radiation in sunlight. The technique developed here to quantify and subtract the UV contribution to the measured tooth is currently limited to cumulative dose measurements with a component of UV equivalent dose equal to or greater than 300 mGy. PMID:20065706
NASA Astrophysics Data System (ADS)
Zhang, Yun; Okubo, R.; Hirano, M.; Hirano, T.
2009-04-01
We report on a measurement of entanglement in the time domain. The entanglement is examined by the Duan-Simon criteria. We obtained Duan-Simon criteria of Δ2(x1-x2)+Δ2(p1+p2) = 1.4<2 without optimal gain and Δ2(x1-x2)+Δ2(p1+p2) = 1.2<2 with optimal gain, respectively. This opens the way to realize both efficient and truly causal EPR paradox.
Short-arc orbit determination using coherent X-band ranging data
NASA Technical Reports Server (NTRS)
Thurman, S. W.; Mcelrath, T. P.; Pollmeier, V. M.
1992-01-01
The use of X-band frequencies in ground-spacecraft and spacecraft-ground telecommunication links for current and future robotic interplanetary missions makes it possible to perform ranging measurements of greater accuracy than previously obtained. It is shown that ranging data of sufficient accuracy, when acquired from multiple stations, can sense the geocentric angular position of a distant spacecraft. The application of high-accuracy S/X-band and X-band ranging to orbit determination with relatively short data arcs is investigated in planetary approach and encounter scenarios. Actual trajectory solutions for the Ulysses spacecraft constructed from S/X-band ranging and Doppler data are presented; error covariance calculations are used to predict the performance of X-band ranging and Doppler data. The Ulysses trajectory solutions indicate that the aim point for the spacecraft's February 1992 Jupiter encounter was predicted to a geocentric accuracy of 0.20 to 0.23/microrad. Explicit modeling of range bias parameters for each station pass is shown to largely remove systematic ground system calibration errors and transmission media effects from the Ulysses range measurements, which would otherwise corrupt the angle finding capabilities of the data. The Ulysses solutions were found to be reasonably consistent with the theoretical results, which suggest that angular accuracies of 0.08 to 0.1/microrad are achievable with X-band ranging.
Chirp echo Fourier transform EPR-detected NMR.
Wili, Nino; Jeschke, Gunnar
2018-04-01
A new ultra-wide band (UWB) pulse EPR method is introduced for observing all nuclear frequencies of a paramagnetic center in a single shot. It is based on burning spectral holes with a high turning angle (HTA) pulse that excites forbidden transitions and subsequent detection of the hole pattern by a chirp echo. We term this method Chirp Echo Epr SpectroscopY (CHEESY)-detected NMR. The approach is a revival of FT EPR-detected NMR. It yields similar spectra and the same type of information as electron-electron double resonance (ELDOR)-detected NMR, but with a multiplex advantage. We apply CHEESY-detected NMR in Q band to nitroxides and correlate the hyperfine spectrum to the EPR spectrum by varying the frequency of the HTA pulse. Furthermore, a selective π pulse before the HTA pulse allows for detecting hyperfine sublevel correlations between transitions of one nucleus and for elucidating the coupling regime, the same information as revealed by the HYSCORE experiment. This is demonstrated on hexaaquamanganese(II). We expect that CHEESY-detected NMR is generally applicable to disordered systems and that our results further motivate the development of EPR spectrometers capable of coherent UWB excitation and detection, especially at higher fields and frequencies. Copyright © 2018 The Author(s). Published by Elsevier Inc. All rights reserved.
Chirp echo Fourier transform EPR-detected NMR
NASA Astrophysics Data System (ADS)
Wili, Nino; Jeschke, Gunnar
2018-04-01
A new ultra-wide band (UWB) pulse EPR method is introduced for observing all nuclear frequencies of a paramagnetic center in a single shot. It is based on burning spectral holes with a high turning angle (HTA) pulse that excites forbidden transitions and subsequent detection of the hole pattern by a chirp echo. We term this method Chirp Echo Epr SpectroscopY (CHEESY)-detected NMR. The approach is a revival of FT EPR-detected NMR. It yields similar spectra and the same type of information as electron-electron double resonance (ELDOR)-detected NMR, but with a multiplex advantage. We apply CHEESY-detected NMR in Q band to nitroxides and correlate the hyperfine spectrum to the EPR spectrum by varying the frequency of the HTA pulse. Furthermore, a selective π pulse before the HTA pulse allows for detecting hyperfine sublevel correlations between transitions of one nucleus and for elucidating the coupling regime, the same information as revealed by the HYSCORE experiment. This is demonstrated on hexaaquamanganese(II). We expect that CHEESY-detected NMR is generally applicable to disordered systems and that our results further motivate the development of EPR spectrometers capable of coherent UWB excitation and detection, especially at higher fields and frequencies.
Block 3 X-band receiver-exciter
NASA Technical Reports Server (NTRS)
Johns, C. E.
1987-01-01
The development of an X-band exciter, for use in the X-Band Uplink Subsystem, was completed. The exciter generates the drive signal for the X-band transmitter and also generates coherent test signals for the S- and X-band Block 3 translator and a Doppler reference signal for the Doppler extractor system. In addition to the above, the exciter generates other reference signals that are described. Also presented is an overview of the exciter design and some test data taken on the prototype. A brief discussion of the Block 3 Doppler extractor is presented.
DOE Office of Scientific and Technical Information (OSTI.GOV)
OShea, J.J.; Brazel, E.G.; Rubin, M.E.
1997-07-01
We report an extensive investigation of semiconductor band-structure effects in single-barrier Al{sub x}Ga{sub 1{minus}x}As/GaAs heterostructures using ballistic-electron-emission spectroscopy (BEES). The transport mechanisms in these single-barrier structures were studied systematically as a function of temperature and Al composition over the full compositional range (0{le}x{le}1). The initial ({Gamma}) BEES thresholds for Al{sub x}Ga{sub 1{minus}x}As single barriers with 0{le}x{le}0.42 were extracted using a model which includes the complete transmission probability of the metal-semiconductor interface and the semiconductor heterostructure. Band offsets measured by BEES are in good agreement with previous measurements by other techniques which demonstrates the accuracy of this technique. BEES measurements atmore » 77 K give the same band-offset values as at room temperature. When a reverse bias is applied to the heterostructures, the BEES thresholds shift to lower voltages in good agreement with the expected bias-induced band-bending. In the indirect band-gap regime ({ital x}{gt}0.45), spectra show a weak ballistic-electron-emission microscopy current contribution due to intervalley scattering through Al{sub x}Ga{sub 1{minus}x}As {ital X} valley states. Low-temperature spectra show a marked reduction in this intervalley current component, indicating that intervalley phonon scattering at the GaAs/Al{sub x}Ga{sub 1{minus}x}As interface produces a significant fraction of this{ital X} valley current. A comparison of the BEES thresholds with the expected composition dependence of the Al{sub x}Ga{sub 1{minus}x}As {Gamma}, {ital L}, and {ital X} points yields good agreement over the entire composition range. {copyright} {ital 1997} {ital The American Physical Society}« less
Spin-Label Oximetry at Q- and W-Band
Subczynski, W.K.; Mainali, L.; Camenisch, T.G.; Froncisz, W.; Hyde, J.S.
2011-01-01
Spin-lattice relaxation times (T1s) of both small water-soluble spin labels in the aqueous phase as well as lipid-type spin labels in membranes increase when the microwave frequency increases from 2 to 35 GHz (Hyde et al., J. Phys. Chem. B 108 [2004] 9524–9529). The T1 measured at W-band (94 GHz) for the water-soluble spin labels CTPO and TEMPONE (Froncisz et al., J. Magn. Reson. 193 [2008] 297–304) is, however, shorter than when measured at Q-band (35 GHz). In this paper, the decreasing trends at W-band have been confirmed for commonly used lipid-type spin labels in model membranes. It is concluded that the longest values of T1 will generally be found at Q-band, noting that long values are advantageous for measurement of bimolecular collisions with oxygen. The contribution of dissolved molecular oxygen to the relaxation rate was found to be independent of microwave frequency up to 94 GHz for lipid-type spin labels in membranes. This contribution is expressed in terms of the oxygen transport parameter W = T1−1(Air) − T1−1(N2), which is a function of both concentration and translational diffusion of oxygen in the local environment of a spin label. The new capabilities in measurement of the oxygen transport parameter using saturation-recovery (SR) EPR at Q- and W-band have been demonstrated in saturated (DMPC) and unsaturated (POPC) lipid bilayer membranes with the use of stearic acid (n-SASL) and phosphatidylcholine (n-PC) spin labels, and compared with results obtained earlier at X-band. SR EPR spin-label oximetry at Q- and W-band has the potential to be a powerful tool for studying samples of small volume, ~30 nL. These benefits, together with other factors such as a higher resonator efficiency parameter and a new technique for canceling free induction decay signals, are discussed. PMID:21277814
Wei, Wei; Qin, Zhixin; Fan, Shunfei; Li, Zhiwei; Shi, Kai; Zhu, Qinsheng; Zhang, Guoyi
2012-10-10
A sample of the β-Ga2O3/wurtzite GaN heterostructure has been grown by dry thermal oxidation of GaN on a sapphire substrate. X-ray diffraction measurements show that the β-Ga2O3 layer was formed epitaxially on GaN. The valence band offset of the β-Ga2O3/wurtzite GaN heterostructure is measured by X-ray photoelectron spectroscopy. It is demonstrated that the valence band of the β-Ga2O3/GaN structure is 1.40 ± 0.08 eV.
EPR and optical investigations of LaMgAl{sub 11}O{sub 19}:Cr{sup 3+} phosphor
DOE Office of Scientific and Technical Information (OSTI.GOV)
Singh, Vijay, E-mail: vijayjiin2006@yahoo.com; Sivaramaiah, G.; Rao, J.L.
2014-12-15
Graphical abstract: The EPR spectrum of as-prepared LaMgAl{sub 11}O{sub 19}:Cr{sup 3+} phosphor at 110 K. - Highlights: • Using the combustion synthesis, LaMgAl{sub 11}O{sub 19}:Cr{sup 3+} phosphor has been prepared in a few minutes. • Optical investigation indicates that Cr{sup 3+} ions are present in octahedral symmetry. • The EPR signals indicate that exchange coupled Cr{sup 3+}–Cr{sup 3+} ion pairs in weakly distorted sites. - Abstract: The LaMgAl{sub 11}O{sub 19}:Cr{sup 3+} phosphor has been prepared by a low-temperature combustion synthesis method. As-prepared combustion synthesized powder was characterized using powder X-ray diffraction (XRD), diffuse reflectance (DRS), electron paramagnetic resonance (EPR) andmore » photoluminescence (PL) studies. The X-ray diffraction pattern reveals crystalline hexagonal phases. The UV–vis diffuse reflectance spectrum exhibits three broad bands characteristic of Cr{sup 3+} ions in octahedral symmetry. The EPR spectrum exhibits several resonance signals. The signals with the effective g values at g = 4.84, 3.64 and 2.26 have been attributed to the isolated Cr{sup 3+} ions. The signal with the effective g value at g = 1.94 has been attributed to exchange coupled Cr{sup 3+}–Cr{sup 3+} ion pairs. The PL studies exhibit several bands characteristic of Cr{sup 3+} ions in octahedral symmetry.« less
Cardon, Thomas B; Tiburu, Elvis K; Lorigan, Gary A
2003-03-01
Our lab is developing a spin-labeled EPR spectroscopic technique complementary to solid-state NMR studies to study the structure, orientation, and dynamics of uniaxially aligned integral membrane proteins inserted into magnetically aligned discotic phospholipid bilayers, or bicelles. The focus of this study is to optimize and understand the mechanisms involved in the magnetic alignment process of bicelle disks in weak magnetic fields. Developing experimental conditions for optimized magnetic alignment of bicelles in low magnetic fields may prove useful to study the dynamics of membrane proteins and its interactions with lipids, drugs, steroids, signaling events, other proteins, etc. In weak magnetic fields, the magnetic alignment of Tm(3+)-doped bicelle disks was thermodynamically and kinetically very sensitive to experimental conditions. Tm(3+)-doped bicelles were magnetically aligned using the following optimized procedure: the temperature was slowly raised at a rate of 1.9K/min from an initial temperature being between 298 and 307K to a final temperature of 318K in the presence of a static magnetic field of 6300G. The spin probe 3beta-doxyl-5alpha-cholestane (cholestane) was inserted into the bicelle disks and utilized to monitor bicelle alignment by analyzing the anisotropic hyperfine splitting for the corresponding EPR spectra. The phases of the bicelles were determined using solid-state 2H NMR spectroscopy and compared with the corresponding EPR spectra. Macroscopic alignment commenced in the liquid crystalline nematic phase (307K), continued to increase upon slowly raising the temperature, and was well-aligned in the liquid crystalline lamellar smectic phase (318K).
NASA Astrophysics Data System (ADS)
Rakvin, B.; Carić, D.; Kveder, M.
2018-02-01
The microwave magnetic field strength, B1, in the cavity of a conventional continuous wave electron paramagnetic resonance, CW-EPR, spectrometer was measured by employing modulation sidebands, MS, in the EPR spectrum. MS spectrum in CW-EPR is produced by applying the modulation frequency, ωrf, which exceeds the linewidth, δB, given in frequency units. An amplitude-modulated CW-EPR, AM-CW-EPR, was selected as detection method. Theoretical description of AM-CW-EPR spectrum was modified by adding Bloch-Siegert-like shift obtained by taking into account the cumulative effect of the non-resonant interactions between the driving fields and the spin system. This approach enables to enhance the precision of B1 measurement. In order to increase the sensitivity of the method when saturation effects, due to higher intensity of B1, decrease the resolution of AM-CW-EPR spectrum, detection at the second harmonic of CW-EPR has been employed.
Rakvin, B; Carić, D; Kveder, M
2018-02-01
The microwave magnetic field strength, B 1 , in the cavity of a conventional continuous wave electron paramagnetic resonance, CW-EPR, spectrometer was measured by employing modulation sidebands, MS, in the EPR spectrum. MS spectrum in CW-EPR is produced by applying the modulation frequency, ω rf , which exceeds the linewidth, δB, given in frequency units. An amplitude-modulated CW-EPR, AM-CW-EPR, was selected as detection method. Theoretical description of AM-CW-EPR spectrum was modified by adding Bloch-Siegert-like shift obtained by taking into account the cumulative effect of the non-resonant interactions between the driving fields and the spin system. This approach enables to enhance the precision of B 1 measurement. In order to increase the sensitivity of the method when saturation effects, due to higher intensity of B 1 , decrease the resolution of AM-CW-EPR spectrum, detection at the second harmonic of CW-EPR has been employed. Copyright © 2018 Elsevier Inc. All rights reserved.
Georgieva, Ekaterina; Zhelev, Zhivko; Aoki, Ichio; Bakalova, Rumiana; Higashi, Tatsuya
2016-10-01
The present study describes a new approach for direct imaging of redox status in live cells using paramagnetic spin-probes, which allows evaluation of the level of oxidative stress due to overproduction of superoxide. The method is based on redox cycling of cell/mitochondria-penetrating nitroxide radicals (e.g. mito-TEMPO) and their electron-paramagnetic resonance (EPR) contrast, which makes them useful molecular sensors for analysis of redox status and oxidative stress in cells and tissues. Oxidative stress was induced in normal human lymphocytes by treatment with 2-methoxyestradiol and rotenone (ME/Rot) at different concentrations. This combination provokes mitochondrial dysfunction, which is accompanied by overproduction of superoxide. The EPR measurements were performed in dynamics on X-Band spectrometer after addition of mito-TEMPO to cell suspensions. The intensity of the EPR signal in untreated cells decreased significantly, which indicates a conversion of paramagnetic mito-TEMPO to its non-contrast diamagnetic form (hydroxylamine - mito-TEMPOH) due to reduction. In ME/Rot-treated cells, the signal decreased more slowly and to a lower level with increasing the concentration of ME/Rot. These data indicate an induction of oxidative stress in the cells in a concentration-dependent manner. A very good positive correlation between the intensity of EPR signal of mito-TEMPO and the intracellular level of superoxide was found, analyzed by conventional dihydroethidium test (R=0.9143, p<0.001). In conclusion, our study demonstrated that cell-penetrating paramagnetic spin-probes, such as mito-TEMPO, are valuable tools for EPR imaging of the superoxide level in live cells, as well as for EPR imaging of mitochondrial dysfunction and metabolic activity, accompanied by superoxide imbalance. Copyright© 2016 International Institute of Anticancer Research (Dr. John G. Delinassios), All rights reserved.
2012-01-01
A sample of the β-Ga2O3/wurtzite GaN heterostructure has been grown by dry thermal oxidation of GaN on a sapphire substrate. X-ray diffraction measurements show that the β-Ga2O3 layer was formed epitaxially on GaN. The valence band offset of the β-Ga2O3/wurtzite GaN heterostructure is measured by X-ray photoelectron spectroscopy. It is demonstrated that the valence band of the β-Ga2O3/GaN structure is 1.40 ± 0.08 eV. PMID:23046910
X-Band CubeSat Communication System Demonstration
NASA Technical Reports Server (NTRS)
Altunc, Serhat; Kegege, Obadiah; Bundick, Steve; Shaw, Harry; Schaire, Scott; Bussey, George; Crum, Gary; Burke, Jacob C.; Palo, Scott; O'Conor, Darren
2015-01-01
Today's CubeSats mostly operate their communications at UHF- and S-band frequencies. UHF band is presently crowded, thus downlink communications are at lower data rates due to bandwidth limitations and are unreliable due to interference. This research presents an end-to-end robust, innovative, compact, efficient and low cost S-band uplink and X-band downlink CubeSat communication system demonstration between a balloon and a Near Earth Network (NEN) ground system. Since communication systems serve as umbilical cords for space missions, demonstration of this X-band communication system is critical for successfully supporting current and future CubeSat communication needs. This research has three main objectives. The first objective is to design, simulate, and test a CubeSat S- and X-band communication system. Satellite Tool Kit (STK) dynamic link budget calculations and HFSS Simulations and modeling results have been used to trade the merit of various designs for small satellite applications. S- and X-band antennas have been tested in the compact antenna test range at Goddard Space Flight Center (GSFC) to gather radiation pattern data. The second objective is simulate and test a CubeSat compatible X-band communication system at 12.5Mbps including S-band antennas, X-band antennas, Laboratory for Atmospheric and Space Physics (LASP) /GSFC transmitter and an S-band receiver from TRL-5 to TRL-8 by the end of this effort. Different X-band communication system components (antennas, diplexers, etc.) from GSFC, other NASA centers, universities, and private companies have been investigated and traded, and a complete component list for the communication system baseline has been developed by performing analytical and numerical analysis. This objective also includes running simulations and performing trades between different X-band antenna systems to optimize communication system performance. The final objective is to perform an end-to-end X-band CubeSat communication system
DOE Office of Scientific and Technical Information (OSTI.GOV)
Allen, Kenneth W., E-mail: kenneth.allen@gtri.gatech.edu; Scott, Mark M.; Reid, David R.
In this work, we present a new X-band waveguide (WR90) measurement method that permits the broadband characterization of the complex permittivity for low dielectric loss tangent material specimens with improved accuracy. An electrically long polypropylene specimen that partially fills the cross-section is inserted into the waveguide and the transmitted scattering parameter (S{sub 21}) is measured. The extraction method relies on computational electromagnetic simulations, coupled with a genetic algorithm, to match the experimental S{sub 21} measurement. The sensitivity of the technique to sample length was explored by simulating specimen lengths from 2.54 to 15.24 cm, in 2.54 cm increments. Analysis ofmore » our simulated data predicts the technique will have the sensitivity to measure loss tangent values on the order of 10{sup −3} for materials such as polymers with relatively low real permittivity values. The ability to accurately characterize low-loss dielectric material specimens of polypropylene is demonstrated experimentally. The method was validated by excellent agreement with a free-space focused-beam system measurement of a polypropylene sheet. This technique provides the material measurement community with the ability to accurately extract material properties of low-loss material specimen over the entire X-band range. This technique could easily be extended to other frequency bands.« less
EPR of radiation defects in lithium-oxyfluoride glass ceramics
NASA Astrophysics Data System (ADS)
Fedotovs, A.; Rogulis, U.; Sarakovskis, A.; Dimitrocenko, L.
2010-11-01
We studied oxyfluoride composites based on lithium silicate glasses with yttrium fluorides and rare-earth dopants. The electron paramagnetic resonance (EPR) has been used to obtain information about radiation induced defects in these materials. Spectra have been measured before and after X-ray irradiation at room temperature and at liquid nitrogen temperature. Fluoride crystallites within samples were created by means of thermal treatment at specific temperatures. EPR spectra of radiation induced defects in oxyfluoride glass ceramics, in which crystallites have not been yet created, show no explicit hfs interaction of fluorine nuclei. However, in glass ceramics, which already contains fluoride crystallites, the hfs characteristic to fluorine nuclei appears in the EPR spectra. EPR hyperfine structure could be explained within a model of an F-type centre in YF3 crystalline phase.
W-band PELDOR with 1 kW microwave power: molecular geometry, flexibility and exchange coupling.
Reginsson, Gunnar W; Hunter, Robert I; Cruickshank, Paul A S; Bolton, David R; Sigurdsson, Snorri Th; Smith, Graham M; Schiemann, Olav
2012-03-01
A technique that is increasingly being used to determine the structure and conformational flexibility of biomacromolecules is Pulsed Electron-Electron Double Resonance (PELDOR or DEER), an Electron Paramagnetic Resonance (EPR) based technique. At X-band frequencies (9.5 GHz), PELDOR is capable of precisely measuring distances in the range of 1.5-8 nm between paramagnetic centres but the orientation selectivity is weak. In contrast, working at higher frequencies increases the orientation selection but usually at the expense of decreased microwave power and PELDOR modulation depth. Here it is shown that a home-built high-power pulsed W-band EPR spectrometer (HiPER) with a large instantaneous bandwidth enables one to achieve PELDOR data with a high degree of orientation selectivity and large modulation depths. We demonstrate a measurement methodology that gives a set of PELDOR time traces that yield highly constrained data sets. Simulating the resulting time traces provides a deeper insight into the conformational flexibility and exchange coupling of three bisnitroxide model systems. These measurements provide strong evidence that W-band PELDOR may prove to be an accurate and quantitative tool in assessing the relative orientations of nitroxide spin labels and to correlate those orientations to the underlying biological structure and dynamics. Copyright © 2012 Elsevier Inc. All rights reserved.
Operando X-ray absorption and EPR evidence for a single electron redox process in copper catalysis
Lu, Qingquan; Zhang, Jian; Peng, Pan; ...
2015-05-26
An unprecedented single electron redox process in copper catalysis is confirmed using operando X-ray absorption and EPR spectroscopies. The oxidation state of the copper species in the interaction between Cu(II) and a sulfinic acid at room temperature, and the accurate characterization of the formed Cu(I) are clearly shown using operando X-ray absorption and EPR evidence. Further investigation of anion effects on Cu(II) discloses that bromine ions can dramatically increase the rate of the redox process. Moreover, it is proven that the sulfinic acids are converted into sulfonyl radicals, which can be trapped by 2-arylacrylic acids and various valuable β-keto sulfonesmore » are synthesized with good to excellent yields under mild conditions.« less
Time-resolved EPR study of singlet oxygen in the gas phase.
Ruzzi, Marco; Sartori, Elena; Moscatelli, Alberto; Khudyakov, Igor V; Turro, Nicholas J
2013-06-27
X-band EPR spectra of singlet O2((1)Δg) and triplet O2((3)Σg(-)) were observed in the gas phase under low molecular-oxygen pressures PO2 = 0.175-0.625 Torr, T = 293-323 K. O2((1)Δg) was produced by quenching of photogenerated triplet sensitizers naphthalene C8H10, perdeuterated naphthalene, and perfluoronaphthalene in the gas phase. The EPR spectrum of O2((1)Δg) was also observed under microwave discharge. Integrated intensities and line widths of individual components of the EPR spectrum of O2((3)Σg(-)) were used as internal standards for estimating the concentration of O2 species and PO2 in the EPR cavity. Time-resolved (TR) EPR experiments of C8H10 were the main focus of this Article. Pulsed irradiation of C8H10 in the presence of O2((3)Σg(-)) allowed us to determine the kinetics of formation and decay for each of the four components of the O2((1)Δg) EPR signal, which lasted for only a few seconds. We found that the kinetics of EPR-component decay fit nicely to a biexponential kinetics law. The TR EPR 2D spectrum of the third component of the O2((1)Δg) EPR spectrum was examined in experiments using C8H10. This spectrum vividly presents the time evolution of an EPR component. The largest EPR signal and the longest lifetime of O2((1)Δg), τ = 0.4 s, were observed at medium pressure PO2 = 0.4 Torr, T = 293 K. The mechanism of O2((1)Δg) decay in the presence of photosensitizers is discussed. EPR spectra of O2((1)Δg) evidence that the spin-rotational states of O2((1)Δg) are populated according to Boltzmann distribution in the studied time range of 10-100 ms. We believe that this is the first report dealing with the dependence of O2((1)Δg) EPR line width on PO2 and T.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Sutton, Kristin A.; Black, Paul J.; Mercer, Kermit R.
2013-12-01
Electron paramagnetic resonance (EPR) and online UV–visible absorption microspectrophotometry with X-ray crystallography have been used in a complementary manner to follow X-ray-induced disulfide-bond cleavage, to confirm a multi-track radiation-damage process and to develop a model of that process. Electron paramagnetic resonance (EPR) and online UV–visible absorption microspectrophotometry with X-ray crystallography have been used in a complementary manner to follow X-ray-induced disulfide-bond cleavage. Online UV–visible spectroscopy showed that upon X-irradiation, disulfide radicalization appeared to saturate at an absorbed dose of approximately 0.5–0.8 MGy, in contrast to the saturating dose of ∼0.2 MGy observed using EPR at much lower dose rates. Themore » observations suggest that a multi-track model involving product formation owing to the interaction of two separate tracks is a valid model for radiation damage in protein crystals. The saturation levels are remarkably consistent given the widely different experimental parameters and the range of total absorbed doses studied. The results indicate that even at the lowest doses used for structural investigations disulfide bonds are already radicalized. Multi-track considerations offer the first step in a comprehensive model of radiation damage that could potentially lead to a combined computational and experimental approach to identifying when damage is likely to be present, to quantitate it and to provide the ability to recover the native unperturbed structure.« less
NASA Astrophysics Data System (ADS)
Subbulakshmi, N.; Kumar, M. Saravana; Sheela, K. Juliet; Krishnan, S. Radha; Shanmugam, V. M.; Subramanian, P.
2017-12-01
Electron Paramagnetic Resonance (EPR) spectroscopic studies of VO2+ ions as paramagnetic impurity in Lithium Sodium Acid Phthalate (LiNaP) single crystal have been done at room temperature on X-Band microwave frequency. The lattice parameter values are obtained for the chosen system from Single crystal X-ray diffraction study. Among the number of hyperfine lines in the EPR spectra only two sets are reported from EPR data. The principal values of g and A tensors are evaluated for the two different VO2+ sites I and II. They possess the crystalline field around the VO2+ as orthorhombic. Site II VO2+ ion is identified as substitutional in place of Na1 location and the other site I is identified as interstitial location. For both sites in LiNaP, VO2+ are identified in octahedral coordination with tetragonal distortion as seen from the spin Hamiltonian parameter values. The ground state of vanadyl ion in the LiNaP single crystal is dxy. Using optical absorption data the octahedral and tetragonal parameters are calculated. By correlating EPR and optical data, the molecular orbital bonding parameters have been discussed for both sites.
Ramos, Paweł; Pilawa, Barbara
2016-06-24
Free radicals formed during thermal sterilization of the Ungentum ophthalmicum were examined by an X-band EPR spectroscopy. The influence of storage time (15 min; 1, 2 and 3 days after heating) on free radical properties and concentrations in this sample was determined. Thermal sterilization was done according to the pharmaceutical norms. The first-derivative EPR spectra with g-values about 2 were measured with magnetic modulation of 100 kHz in the range of microwave power 2.2-70 mW. The changes of amplitudes (A) and linewidths (ΔB pp ) with microwave powers were evaluated. Free radicals in concentration ∼10 17 spin/g were formed during heating of the tested Ungentum. Free radical concentration decreased with increase in storage time, and reached values ∼10 17 spin/g after 3 days from sterilization. The tested U. ophthalmicum should not be sterilized at a temperature of 160 °C because of the free radicals formation, or it should be used 3 days after heating, when free radicals were considerably quenched. Free radical properties remain unchanged during storage of the Ungentum. The EPR lines of the U. ophthalmicum were homogeneously broadened and their linewidths (ΔB pp ) increased with increase in microwave power. EPR spectroscopy is useful to examine free radicals to optimize sterilization process and storage conditions of ophthalmologic samples.
Application of EPR spectroscopy to the examination of pro-oxidant activity of coffee.
Krakowian, Daniel; Skiba, Dominik; Kudelski, Adam; Pilawa, Barbara; Ramos, Paweł; Adamczyk, Jakub; Pawłowska-Góral, Katarzyna
2014-05-15
Free radicals present in coffee may be responsible for exerting toxic effects on an organism. The objectives of this work were to compare free radicals properties and concentrations in different commercially available coffees, in solid and liquid states, and to determine the effect of roasting on the formation of free radicals in coffee beans of various origins. The free radicals content of 15 commercially available coffees (solid and liquid) was compared and the impact of processing examined using electron paramagnetic resonance (EPR) spectroscopy at X-band (9.3 GHz). First derivative EPR spectra were measured at microwave power in the range of 0.7-70 mW. The following parameters were calculated for EPR spectra: amplitude (A), integral intensity (I), and line-width (ΔBpp); g-Factor was obtained from resonance condition. Our study showed that free radicals exist in green coffee beans (10(16) spin/g), roasted coffee beans (10(18) spin/g), and in commercially available coffee (10(17)-10(18) spin/g). Free radical concentrations were higher in solid ground coffee than in instant or lyophilised coffee. Continuous microwave saturation indicated homogeneous broadening of EPR lines from solid and liquid commercial coffee samples as well as green and roasted coffee beans. Slow spin-lattice relaxation processes were found to be present in all coffee samples tested, solid and liquid commercial coffees as well as green and roasted coffee beans. Higher free radicals concentrations were obtained for both the green and roasted at 240 °C coffee beans from Peru compared with those originating from Ethiopia, Brazil, India, or Colombia. Moreover, more free radicals occurred in Arabica coffee beans roasted at 240 °C than Robusta. EPR spectroscopy is a useful method of examining free radicals in different types of coffee. Copyright © 2013 Elsevier Ltd. All rights reserved.
NASA Astrophysics Data System (ADS)
Mayer, Marie Annette
New technologies motivate the development of new semiconducting materials, for which structural, electrical and chemical properties are not well understood. In addition to new materials systems, there are huge opportunities for new applications, especially in solar energy conversion. In this dissertation I explore the role of band structure engineering of semiconducting oxides for solar energy. Due to the abundance and electrochemical stability of oxides, the appropriate modification could make them appealing for applications in both photovoltaics and photoelectrochemical hydrogen production. This dissertation describes the design, synthesis and evaluation of the alloy ZnO1-xSe x for these purposes. I review several methods of band structure engineering including strain, quantum confinement and alloying. A detailed description of the band anticrossing (BAC) model for highly mismatched alloys is provided, including the derivation of the BAC model as well as recent work and potential applications. Thin film ZnOxSe1-x samples are grown by pulsed laser deposition (PLD). I describe in detail the effect of growth conditions (temperature, pressure and laser fluence) on the chemistry, structure and optoelectronic properties of ZnOxSe1-x. The films are grown using different combinations of PLD conditions and characterized with a variety of techniques. Phase pure films with low roughness and high crystallinity were obtained at temperatures below 450¢ªC, pressures less than 10-4 Torr and laser fluences on the order of 1.5 J/cm 2. Electrical conduction was still observed despite heavy concentrations of grain boundaries. The band structure of ZnO1-xSex is then examined in detail. The bulk electron affinity of a ZnO thin film was measured to be 4.5 eV by pinning the Fermi level with native defects. This is explained in the framework of the amphoteric defect model. A shift in the ZnO1-xSe x valence band edge with x is observed using synchrotron x-ray absorption and emission
Valence band offsets of Sc x Ga1-x N/AlN and Sc x Ga1-x N/GaN heterojunctions
NASA Astrophysics Data System (ADS)
Tsui, H. C. L.; Goff, L. E.; Palgrave, R. G.; Beere, H. E.; Farrer, I.; Ritchie, D. A.; Moram, M. A.
2016-07-01
The valence band offsets of Sc x Ga1-x N/AlN heterojunctions were measured by x-ray photoelectron spectroscopy (XPS) and were found to increase from 0.42 eV to 0.95 eV as the Sc content x increased from 0 to 0.15. The increase in valence band offset with increasing x is attributed to the corresponding increase in spontaneous polarization of the wurtzite structure. The Sc x Ga1-x N/AlN heterojunction is type I, similar to other III-nitride-based heterojunctions. The data also indicate that a type II staggered heterojunction, which can enhance spatial charge separation, could be formed if Sc x Ga1-x N is grown on GaN.
Ceccon, Alberto; Schmidt, Thomas; Tugarinov, Vitali; Kotler, Samuel A; Schwieters, Charles D; Clore, G Marius
2018-05-23
Lipid-based micellar nanoparticles promote aggregation of huntingtin exon-1 peptides. Here we characterize the interaction of two such peptides, htt NT Q 7 and htt NT Q 10 comprising the N-terminal amphiphilic domain of huntingtin followed by 7 and 10 glutamine repeats, respectively, with 8 nm lipid micelles using NMR chemical exchange saturation transfer (CEST), circular dichroism and pulsed Q-band EPR. Exchange between free and micelle-bound htt NT Q n peptides occurs on the millisecond time scale with a K D ∼ 0.5-1 mM. Upon binding micelles, residues 1-15 adopt a helical conformation. Oxidation of Met 7 to a sulfoxide reduces the binding affinity for micelles ∼3-4-fold and increases the length of the helix by a further two residues. A structure of the bound monomer unit is calculated from the backbone chemical shifts of the micelle-bound state obtained from CEST. Pulsed Q-band EPR shows that a monomer-dimer equilibrium exists on the surface of the micelles and that the two helices of the dimer adopt a parallel orientation, thereby bringing two disordered polyQ tails into close proximity which may promote aggregation upon dissociation from the micelle surface.
Nakagawa, Kouichi; Matsumoto, Kazuhiro; Chaiserm, Nattakan; Priprem, Aroonsri
2017-01-01
We investigated stable organic radicals formed in response to cold stratification in 'Fuji' apple seeds using X-band (9 GHz) electron paramagnetic resonance (EPR) technique. This technique primarily detected two paramagnetic species in each seed. These two different radical species were assigned as a stable organic radical and Mn 2+ species based on the g values and hyperfine components. Signal from the stable radicals was noted at a g value of about 2.00 and was strong and relatively stable. Significant radical intensity changes were observed in apple seeds on refrigeration along with water supplementation. The strongest radical intensity and a very weak Mn 2+ signal were also observed for the seeds kept in moisture-containing sand in a refrigerator. Noninvasive EPR of the radicals present in each seed revealed that the stable radicals were located primarily in the seed coat. These results indicate that the significant radical intensity changes in apple seeds under refrigeration for at least 90 days followed by water supplementation for one week, can be related to cold stratification of the seeds.
Nakagawa, Kouichi; Maeda, Hayato
2017-02-01
We investigated the location and distribution of paramagnetic species in dry black, brown, and yellow (normal) soybean seeds using electron paramagnetic resonance (EPR), X-band (9 GHz) EPR imaging (EPRI), and HPLC. EPR primarily detected two paramagnetic species in black soybean. These two different radical species were assigned as stable organic radical and Mn 2+ species based on the g values and hyperfine structures. The signal from the stable radical was noted at g ≈ 2.00 and was relatively strong and stable. Subsequent noninvasive two-dimensional (2D) EPRI of the radical present in black soybean revealed that the stable radical was primarily located in the pigmented region of the soybean coat, with very few radicals observed in the soybean cotyledon (interior). Pigments extracted from black soybean were analyzed using HPLC. The major compound was found to be cyanidin-3-glucoside. Multi-EPR and HPLC results indicate that the stable radical was only found within the pigmented region of the soybean coat, and it could be cyanidin-3-glucoside or an oxidative decomposition product.
Performance of a first generation X-band photoelectron rf gun
Limborg-Deprey, C.; Adolphsen, C.; McCormick, D.; ...
2016-05-04
Building more compact accelerators to deliver high brightness electron beams for the generation of high flux, highly coherent radiation is a priority for the photon science community. A relatively straightforward reduction in footprint can be achieved by using high-gradient X-band (11.4 GHz) rf technology. To this end, an X-band injector consisting of a 5.5 cell rf gun and a 1-m long linac has been commissioned at SLAC. It delivers an 85 MeV electron beam with peak brightness somewhat better than that achieved in S-band photoinjectors, such as the one developed for the Linac Coherent Light Source (LCLS). The X-band rfmore » gun operates with up to a 200 MV/m peak field on the cathode, and has been used to produce bunches of a few pC to 1.2 nC in charge. Notably, bunch lengths as short as 120 fs rms have been measured for charges of 5 pC (~3×10 7 electrons), and normalized transverse emittances as small as 0.22 mm-mrad have been measured for this same charge level. Bunch lengths as short as 400 (250) fs rms have been achieved for electron bunches of 100 (20) pC with transverse normalized emittances of 0.7 (0.35) mm-mrad. As a result, we report on the performance and the lessons learned from the operation and optimization of this first generation X-band gun.« less
Performance of a first generation X-band photoelectron rf gun
DOE Office of Scientific and Technical Information (OSTI.GOV)
Limborg-Deprey, C.; Adolphsen, C.; McCormick, D.
Building more compact accelerators to deliver high brightness electron beams for the generation of high flux, highly coherent radiation is a priority for the photon science community. A relatively straightforward reduction in footprint can be achieved by using high-gradient X-band (11.4 GHz) rf technology. To this end, an X-band injector consisting of a 5.5 cell rf gun and a 1-m long linac has been commissioned at SLAC. It delivers an 85 MeV electron beam with peak brightness somewhat better than that achieved in S-band photoinjectors, such as the one developed for the Linac Coherent Light Source (LCLS). The X-band rfmore » gun operates with up to a 200 MV/m peak field on the cathode, and has been used to produce bunches of a few pC to 1.2 nC in charge. Notably, bunch lengths as short as 120 fs rms have been measured for charges of 5 pC (~3×10 7 electrons), and normalized transverse emittances as small as 0.22 mm-mrad have been measured for this same charge level. Bunch lengths as short as 400 (250) fs rms have been achieved for electron bunches of 100 (20) pC with transverse normalized emittances of 0.7 (0.35) mm-mrad. As a result, we report on the performance and the lessons learned from the operation and optimization of this first generation X-band gun.« less
Einstein-Podolsky-Rosen Entanglement of Narrow-Band Photons from Cold Atoms.
Lee, Jong-Chan; Park, Kwang-Kyoon; Zhao, Tian-Ming; Kim, Yoon-Ho
2016-12-16
Einstein-Podolsky-Rosen (EPR) entanglement introduced in 1935 deals with two particles that are entangled in their positions and momenta. Here we report the first experimental demonstration of EPR position-momentum entanglement of narrow-band photon pairs generated from cold atoms. By using two-photon quantum ghost imaging and ghost interference, we demonstrate explicitly that the narrow-band photon pairs violate the separability criterion, confirming EPR entanglement. We further demonstrate continuous variable EPR steering for positions and momenta of the two photons. Our new source of EPR-entangled narrow-band photons is expected to play an essential role in spatially multiplexed quantum information processing, such as, storage of quantum correlated images, quantum interface involving hyperentangled photons, etc.
Einstein-Podolsky-Rosen Entanglement of Narrow-Band Photons from Cold Atoms
NASA Astrophysics Data System (ADS)
Lee, Jong-Chan; Park, Kwang-Kyoon; Zhao, Tian-Ming; Kim, Yoon-Ho
2016-12-01
Einstein-Podolsky-Rosen (EPR) entanglement introduced in 1935 deals with two particles that are entangled in their positions and momenta. Here we report the first experimental demonstration of EPR position-momentum entanglement of narrow-band photon pairs generated from cold atoms. By using two-photon quantum ghost imaging and ghost interference, we demonstrate explicitly that the narrow-band photon pairs violate the separability criterion, confirming EPR entanglement. We further demonstrate continuous variable EPR steering for positions and momenta of the two photons. Our new source of EPR-entangled narrow-band photons is expected to play an essential role in spatially multiplexed quantum information processing, such as, storage of quantum correlated images, quantum interface involving hyperentangled photons, etc.
Simultaneous S- and X-band uplink-downlink performance at DSS 13
NASA Technical Reports Server (NTRS)
Freiley, A. J.
1988-01-01
The Deep Space Station 13 26-meter antenna with the second generation S/X feedcone was tested to determine the dual S- and X-band (2.1 to 2.3 GHz and 7.1 to 8.5 GHz) transmit and receive performance. Measurements were conducted using the 20 kW transmitters at S- and X-band while simultaneously receiving S- and X-band. This system proved to be very quiet compared with the other DSN antennas. Under normal tracking configurations, no noise burst or intermodulation product (IMP) activity was detectable to the -175 dBm level. To prove the instrumentation's ability to detect such phenomena, an IMP generator was introduced onto the system with positive, verifiable results. The IMP occurred at the -162 dBm level, accompanied by moderate noise burst activity, and was readily repeatable. The measurement also showed the possible need for additional fourth channel filtering in the system to reduce the effect of the transmitter power on the low noise amplifiers.
Inverted S-Shaped Compact Antenna for X-Band Applications
Samsuzzaman, M.; Islam, M. T.
2014-01-01
A novel probe-fed compact inverted S-shaped multifrequency patch antenna is designed. By employing two rectangular slots that change the conventional rectangular patch into an inverted S-shaped patch, the antenna is able to operate in triple frequency in the X-band. The performance criteria of the proposed design have been experimentally verified by fabricating a printed prototype. The measured results show that the −10 dB impedance bandwidth of the proposed antenna at lower band is 5.02% (8.69–9.14 GHz), at middle band is 9.13% (10.47–11.48 GHz), and at upper band is 3.79% (11.53–11.98 GHz). Two elliptical slots are introduced in the ground plane to increase the peak gain. The antenna is excited by a simple probe feeding mechanism. The overall antenna dimension is 0.52λ × 0.60λ × 0.046λ at a lower resonance frequency of 9.08 GHz. The antenna configuration and parametric investigation are conducted with the help of the high frequency structural simulator, and a good agreement is achieved between the simulated and measured data. The stable gain, omnidirectional radiation pattern, and consistent radiation efficiency in the achieved operating band make the proposed antenna a suitable candidate for X-band applications. PMID:24895656
NASA Technical Reports Server (NTRS)
Groot, J. S.
1990-01-01
In August 1989 the NASA/JPL airborne P/L/C-band DC-8 SAR participated in several remote sensing campaigns in Europe. Amongst other test sites, data were obtained of the Flevopolder test site in the Netherlands on August the 16th. The Dutch X-band SLAR was flown on the same date and imaged parts of the same area as the SAR. To calibrate the two imaging radars a set of 33 calibration devices was deployed. 16 trihedrals were used to calibrate a part of the SLAR data. This short paper outlines the X-band SLAR characteristics, the experimental set-up and the calibration method used to calibrate the SLAR data. Finally some preliminary results are given.
An EPR methodology for measuring the London penetration depth for the ceramic superconductors
NASA Technical Reports Server (NTRS)
Rakvin, B.; Mahl, T. A.; Dalal, N. S.
1990-01-01
The use is discussed of electron paramagnetic resonance (EPR) as a quick and easily accessible method for measuring the London penetration depth, lambda for the high T(sub c) superconductors. The method utilizes the broadening of the EPR signal, due to the emergence of the magnetic flux lattice, of a free radical adsorbed on the surface of the sample. The second moment, of the EPR signal below T(sub c) is fitted to the Brandt equation for a simple triangular lattice. The precision of this method compares quite favorably with those of the more standard methods such as micro sup(+)SR, Neutron scattering, and magnetic susceptibility.
Water accessibility in a membrane-inserting peptide comparing Overhauser DNP and pulse EPR methods.
Segawa, Takuya F; Doppelbauer, Maximilian; Garbuio, Luca; Doll, Andrin; Polyhach, Yevhen O; Jeschke, Gunnar
2016-05-21
Water accessibility is a key parameter for the understanding of the structure of biomolecules, especially membrane proteins. Several experimental techniques based on the combination of electron paramagnetic resonance (EPR) spectroscopy with site-directed spin labeling are currently available. Among those, we compare relaxation time measurements and electron spin echo envelope modulation (ESEEM) experiments using pulse EPR with Overhauser dynamic nuclear polarization (DNP) at X-band frequency and a magnetic field of 0.33 T. Overhauser DNP transfers the electron spin polarization to nuclear spins via cross-relaxation. The change in the intensity of the (1)H NMR spectrum of H2O at a Larmor frequency of 14 MHz under a continuous-wave microwave irradiation of the nitroxide spin label contains information on the water accessibility of the labeled site. As a model system for a membrane protein, we use the hydrophobic α-helical peptide WALP23 in unilamellar liposomes of DOPC. Water accessibility measurements with all techniques are conducted for eight peptides with different spin label positions and low radical concentrations (10-20 μM). Consistently in all experiments, the water accessibility appears to be very low, even for labels positioned near the end of the helix. The best profile is obtained by Overhauser DNP, which is the only technique that succeeds in discriminating neighboring positions in WALP23. Since the concentration of the spin-labeled peptides varied, we normalized the DNP parameter ϵ, being the relative change of the NMR intensity, by the electron spin concentration, which was determined from a continuous-wave EPR spectrum.
Intercomparison of attenuation correction algorithms for single-polarized X-band radars
NASA Astrophysics Data System (ADS)
Lengfeld, K.; Berenguer, M.; Sempere Torres, D.
2018-03-01
Attenuation due to liquid water is one of the largest uncertainties in radar observations. The effects of attenuation are generally inversely proportional to the wavelength, i.e. observations from X-band radars are more affected by attenuation than those from C- or S-band systems. On the other hand, X-band radars can measure precipitation fields in higher temporal and spatial resolution and are more mobile and easier to install due to smaller antennas. A first algorithm for attenuation correction in single-polarized systems was proposed by Hitschfeld and Bordan (1954) (HB), but it gets unstable in case of small errors (e.g. in the radar calibration) and strong attenuation. Therefore, methods have been developed that restrict attenuation correction to keep the algorithm stable, using e.g. surface echoes (for space-borne radars) and mountain returns (for ground radars) as a final value (FV), or adjustment of the radar constant (C) or the coefficient α. In the absence of mountain returns, measurements from C- or S-band radars can be used to constrain the correction. All these methods are based on the statistical relation between reflectivity and specific attenuation. Another way to correct for attenuation in X-band radar observations is to use additional information from less attenuated radar systems, e.g. the ratio between X-band and C- or S-band radar measurements. Lengfeld et al. (2016) proposed such a method based isotonic regression of the ratio between X- and C-band radar observations along the radar beam. This study presents a comparison of the original HB algorithm and three algorithms based on the statistical relation between reflectivity and specific attenuation as well as two methods implementing additional information of C-band radar measurements. Their performance in two precipitation events (one mainly convective and the other one stratiform) shows that a restriction of the HB is necessary to avoid instabilities. A comparison with vertically pointing
Low-valent low-coordinated manganese(I) ion dimer: a temperature dependent W-band EPR study.
Sorace, Lorenzo; Golze, Christian; Gatteschi, Dante; Bencini, Alessandro; Roesky, Herbert W; Chai, Jianfang; Stückl, A Claudia
2006-01-09
W-Band EPR spectra of [[HC(CMeNAr)(2)]Mn](2) (Ar = 2,6-(i)Pr(2)C(6)H(3)) have been measured at different temperatures. The spectra show a behavior which is typical for an antiferromagnetically coupled dimer with excited states populating upon increasing temperature. By following the intensity variation of the different features of the spectra with temperature, we attributed different groups of resonances to the S = 1, 2, and 3 states of the dimer. Their corresponding spin Hamiltonian parameters were derived from simulations. The zero-field-splitting parameters measured in this way were D(S=1) = 1.57 cm(-1) and E(S=1) = 0.064 cm(-1), D(S=2) = 0.266 cm(-1) and E(S=2) = 0.0045 cm(-1), and D(S=3) = 0.075 cm(-1) and E(S=3) = 0. On the basis of the molecular structure of the system, we could estimate that zero-field splitting (ZFS) is the result of anisotropic exchange and single-ion anisotropic contributions of similar magnitude (|D| approximately 0.2 cm(-1)). These results allow a deeper insight into the electronic structure of the Mn(I) centers in low-coordination environments, further supporting the electronic structure of Mn(I) to be 4s(1)3d(5), as previously indicated by DFT calculations.
A programmable ultra-low noise X-band exciter.
MacMullen, A; Hoover, L R; Justice, R D; Callahan, B S
2001-07-01
A programmable ultra-low noise X-band exciter has been developed using commercial off-the-shelf components. Its phase noise is more than 10 dB below the best available microwave synthesizers. It covers a 7% frequency band with 0.1-Hz resolution. The X-band output at +23 dBm is a combination of signals from an X-band sapphire-loaded cavity oscillator (SLCO), a low noise UHF frequency synthesizer, and special-purpose frequency translation and up-conversion circuitry.
NASA Astrophysics Data System (ADS)
Jin, Jia-Rui; Wu, Shao-Yi; Hong, Jian; Liu, Shi-Nan; Song, Min-Xian; Teng, Bao-Hua; Wu, Ming-He
2017-11-01
The local structures and electron paramagnetic resonance (EPR) parameters for Cu2+ in 59B2O3-10K2O-(30-x)ZnO-xBaO-1CuO (BKZBC) glasses are theoretically investigated with distinct modifier BaO concentrations x (= 0, 6, 12, 18, 24 and 30 mol %). The ? clusters are found to undergo the relative tetragonal elongations of about 13.5 and 5.0% at zero and higher BaO concentrations. The concentration dependences of the measured d-d transition bands, g factors and A// are suitably reproduced from the Fourier type functions or sign functions of the relevant quantities with x by using only six adjustable parameters. The features of the EPR parameters and the local structures of Cu2+ are analysed in a consistent way by considering the differences in the local ligand field strength and electronic cloud admixtures around Cu2+ under addition of Ba2+ with the highest ionicity and polarisability. The present theoretical studies would be helpful to the researches on the structures, optical and EPR properties for the similar potassium barium zinc borate glasses containing copper with variation concentration of modifier BaO.
Hricovíni, Michal; Mazúr, Milan; Sîrbu, Angela; Palamarciuc, Oleg; Arion, Vladimir B; Brezová, Vlasta
2018-03-21
X- and Q-band electron paramagnetic resonance (EPR) spectroscopy was used to characterize polycrystalline Cu(II) complexes that contained sodium 5-sulfonate salicylaldehyde thiosemicarbazones possessing a hydrogen, methyl, ethyl, or phenyl substituent at the terminal nitrogen. The ability of thiosemicarbazone proligands to generate superoxide radical anions and hydroxyl radicals upon their exposure to UVA irradiation in aerated aqueous solutions was evidenced by the EPR spin trapping technique. The UVA irradiation of proligands in neutral or alkaline solutions and dimethylsulfoxide (DMSO) caused a significant decrease in the absorption bands of aldimine and phenolic chromophores. Mixing of proligand solutions with the equimolar amount of copper(II) ions resulted in the formation of 1:1 Cu(II)-to-ligand complex, with the EPR and UV-Vis spectra fully compatible with those obtained for the dissolved Cu(II) thiosemicarbazone complexes. The formation of the complexes fully inhibited the photoinduced generation of reactive oxygen species, and only subtle changes were found in the electronic absorption spectra of the complexes in aqueous and DMSO solutions upon UVA steady-state irradiation. The dark redox activity of copper(II) complexes and proligand/Cu(II) aqueous solutions towards hydrogen peroxide which resulted in the generation of hydroxyl radicals, was confirmed by spin trapping experiments.
Moons, Hans; Łapok, Łukasz; Loas, Andrei; Van Doorslaer, Sabine; Gorun, Sergiu M
2010-10-04
The synthesis, crystal structure, and electronic properties of perfluoro-isopropyl-substituted perfluorophthalocyanine bearing a copper atom in the central cavity (F(64)PcCu) are reported. While most halogenated phthalocyanines do not exhibit long-term order sufficient to form large single crystals, this is not the case for F(64)PcCu. Its crystal structure was determined by X-ray analysis and linked to the electronic properties determined by electron paramagnetic resonance (EPR). The findings are corroborated by density functional theory (DFT) computations, which agree well with the experiment. X-band continuous-wave EPR spectra of undiluted F(64)PcCu powder, indicate the existence of isolated metal centers. The electron-withdrawing effect of the perfluoroalkyl (R(f)) groups significantly enhances the complexes solubility in organic solvents like alcohols, including via their axial coordination. This coordination is confirmed by X-band (1)H HYSCORE experiments and is also seen in the solid state via the X-ray structure. Detailed X-band CW-EPR, X-band Davies and Mims ENDOR, and W-band electron spin-echo-detected EPR studies of F(64)PcCu in ethanol allow the determination of the principal g values and the hyperfine couplings of the metal, nitrogen, and fluorine nuclei. Comparison of the g and metal hyperfine values of F(64)PcCu and other PcCu complexes in different matrices reveals a dominant effect of the matrix on these EPR parameters, while variations in the ring substituents have only a secondary effect. The relatively strong axial coordination occurs despite the diminished covalency of the C-N bonds and potentially weakening Jahn-Teller effects. Surprisingly, natural abundance (13)C HYSCORE signals could be observed for a frozen ethanol solution of F(64)PcCu. The (13)C nuclei contributing to the HYSCORE spectra could be identified as the pyrrole carbons by means of DFT. Finally, (19)F ENDOR and easily observable paramagnetic NMR were found to relate well to the
Band alignment of SiO2/(AlxGa1-x)2O3 (0 ≤ x ≤ 0.49) determined by X-ray photoelectron spectroscopy
NASA Astrophysics Data System (ADS)
Feng, Zhaoqing; Feng, Qian; Zhang, Jincheng; Li, Xiang; Li, Fuguo; Huang, Lu; Chen, Hong-Yan; Lu, Hong-Liang; Hao, Yue
2018-03-01
In this work, we report the investigation of the band alignment of SiO2/(AlxGa1-x)2O3 (0 ≤ x ≤ 0.49) utilizing the high resolution X-ray photoelectron spectroscopy (XPS) measurements. The single crystallinity and orientation of β-(AlxGa1-x)2O3 films grown on sapphire by pulsed laser deposition were studied with the high resolution X-ray diffraction. The Ga 2p3/2 and Si 2p core-level spectra as well as valence band spectra were used in the analysis of band alignment. As the mole fraction x of Al increases from 0 to 0.49, the bandgap and conduction band offset values of SiO2/(AlxGa1-x)2O3 increases from 4.9 to 5.6 eV and from 1.5 to 2.1 eV, respectively, while that of valence band offset decreases from 2.2 to 0.9 eV. From the results obtained, the energy band diagram of the studied SiO2/(AlxGa1-x)2O3 (0 ≤ x ≤ 0.49) interfaces is found to be of type I. Energy band lineups of SiO2/(AlxGa1-x)2O3 were thus determined which can be used as for Ga2O3 based power device technology.
Measurements of Local Strain Variation in Si(1-x)Ge(x)/Si Heterostructures
NASA Technical Reports Server (NTRS)
Bell, L. D.; Kaiser, W. J.; Manion, S. J.; Milliken, S. J.; Pike, W. T.; Fathauer, R. W.
1995-01-01
The energy splitting of the conduction-band minimum of Si(1-x), Ge(x), due to strain has been directly measured by the application of ballistic-electron-emission microscope (BEEM) spectroscopy to Ag/Si(1-x), Ge(x) structures. Experimental values for this conduction-band splitting agree well with calculations. For Au/Si(1-x), Ge(x), however, heterogeneity in the strain of the Si(1-x), Ge(x) layer is introduced by deposition of the Au. This variation is attributed to species interdiffusion, which produces a rough Si(1-x)Ge(x) surface. Preliminary modeling indicates that the observed roughness is consistent with the strain variation measured by BEEM.
NASA Astrophysics Data System (ADS)
Smith, Clare L.; Ankers, Elizabeth; Best, Stephen P.; Gagliardi, Frank; Katahira, Kai; Tsunei, Yseu; Tominaga, Takahiro; Geso, Moshi
2017-12-01
The suitability of IRGANOX®1076 in paraffin wax as a near-tissue equivalent radiation dosimeter was investigated for various radiotherapy beam types; kV and MV X-rays, electrons and protons over clinically-relevant doses (2 -20 Gy). The radical formed upon exposure to ionising radiations was measured by Electron Paramagnetic Resonance (EPR) spectroscopy, and the single peak signal obtained for solid solutions of IRGANOX®1076 in wax is attributed to the phenoxyl radical obtained by net loss of H•. Irradiation of solid IRGANOX®1076 gives a doublet consistent with the formation of the phenol cation radical, obtained by electron loss. Solid solutions of IRGANOX®1076 in paraffin wax give a linear dose response for all types of radiations examined, which was energy independent for MV, electron and proton beams, and energy-dependent for kV X-ray irradiation. Reliable dose measurements were obtained with exposures as low as 2 Gy, and comparisons with alanine wax-pellets containing the same amount of dosimeter material (w/w) gave similar responses for all beam types investigated. Post-irradiation measurements (up to 77 days for proton irradiation for samples stored in the dark and at room temperature) indicate good signal stability with minimal signal fading (between 1.6 to 3.8%). Relative to alanine dosimeters, solid solutions of IRGANOX®1076 in wax give EPR signals with better sensitivity at low dose and do not significantly change with the orientation of the sample. Solid solutions of IRGANOX®1076 are ideal for applications in radiotherapy dosimetry for X-rays and charged particles, as IRGANOX®1076 is relatively cheap, can easily and reproducibly prepared in wax and be moulded to different shapes.
NASA Astrophysics Data System (ADS)
Goswami, B.; Kalita, M.
2014-11-01
The objective of the study is to measure backscattered power of bare soil and vegetation covered soil using X-band scatterometer system with full polarization and various angles during monsoon season and relate backscattered power to the density of vegetation over soil. The measurement was conducted at an experimental field located in the campus of Assam Engineering College, Guwahati, India. The soil sample consists of Silt and Clay in higher proportions as compared to Sand. The scatterometer system consists of dual-polarimetric square horn antennas, Power meter, Klystron, coaxial cables, isolator and waveguide detector. The polarization of the horn antennas as well as the look angle can be changed in the set-up. The backscattering coefficients were calculated by applying a radar equation for the measured values at incident angles between 30° and 60° for full polarization (HH, VV, HV, VH), respectively, and compared with vegetation cover over soil for each scatterometer measurement simultaneously. The VH polarization and 60° look angle are found to be the most suitable combination of configuration of an X-band scatterometer for distinguishing the land cover targets such as bare soil and vegetation covered soil. From the analysis of the results, polarimetric scatterometer data appear to be promising to distinguish the land cover types such as bare soil and soil completely covered by vegetation. The results of this study will help the scientists working in the field of active microwave remote sensing.
Modeling Multi-Bunch X-band Photoinjector Challenges
DOE Office of Scientific and Technical Information (OSTI.GOV)
Marsh, R A; Anderson, S G; Gibson, D J
An X-band test station is being developed at LLNL to investigate accelerator optimization for future upgrades to mono-energetic gamma-ray technology at LLNL. The test station will consist of a 5.5 cell X-band rf photoinjector, single accelerator section, and beam diagnostics. Of critical import to the functioning of the LLNL X-band system with multiple electron bunches is the performance of the photoinjector. In depth modeling of the Mark 1 LLNL/SLAC X-band rf photoinjector performance will be presented addressing important challenges that must be addressed in order to fabricate a multi-bunch Mark 2 photoinjector. Emittance performance is evaluated under different nominal electronmore » bunch parameters using electrostatic codes such as PARMELA. Wake potential is analyzed using electromagnetic time domain simulations using the ACE3P code T3P. Plans for multi-bunch experiments and implementation of photoinjector advances for the Mark 2 design will also be discussed.« less
NASA Astrophysics Data System (ADS)
Agrawal, A. P.; Carnegie, D. W.; Boerner, W.-M.
This paper presents an evaluation of polarimetric rain backscatter measurements collected with coherent dual polarization radar systems in the X (8.9 GHz) and Q (45GHz) bands, the first being operated in a pulsed mode and the second being a FM-CW system. The polarimetric measurement data consisted for each band of fifty files of time-sequential scattering matrix measurements expressed in terms of a linear (H, V) antenna polarization state basis. The rain backscattering takes place in a rain cell defined by the beam widths and down range distances of 275 ft through 325 ft and the scattering matrices were measured far below the hydrometeoric scattering center decorrelation time so that ensemble averaging of time-sequential scattering matrices may be applied. In the data evaluation great care was taken in determining: (1) polarimetric Doppler velocities associated with the motion of descending oscillating raindrops and/or eddies within the moving swaths of coastal rain showers, and (2) also the properties of the associated co/cross-polarization rain clutter nulls and their distributions on the Poincare polarization sphere.
NASA Technical Reports Server (NTRS)
Mysoor, Narayan R.; Perret, Jonathan D.; Kermode, Arthur W.
1991-01-01
The design concepts and measured performance characteristics of an X band (7162 MHz/8415 MHz) breadboard deep space transponder (DST) for future spacecraft applications, with the first use scheduled for the Comet Rendezvous Asteroid Flyby (CRAF) and Cassini missions in 1995 and 1996, respectively. The DST consists of a double conversion, superheterodyne, automatic phase tracking receiver, and an X band (8415 MHz) exciter to drive redundant downlink power amplifiers. The receiver acquires and coherently phase tracks the modulated or unmodulated X band (7162 MHz) uplink carrier signal. The exciter phase modulates the X band (8415 MHz) downlink signal with composite telemetry and ranging signals. The receiver measured tracking threshold, automatic gain control static phase error, and phase jitter characteristics of the breadboard DST are in good agreement with the expected performance. The measured results show a receiver tracking threshold of -158 dBm and a dynamic signal range of 88 dB.
NASA Technical Reports Server (NTRS)
Mysoor, Narayan R.; Perret, Jonathan D.; Kermode, Arthur W.
1992-01-01
The design concepts and measured performance characteristics are summarized of an X band (7162 MHz/8415 MHz) breadboard deep space transponder (DSP) for future spacecraft applications, with the first use scheduled for the Comet Rendezvous Asteroid Flyby (CRAF) and Cassini missions in 1995 and 1996, respectively. The DST consists of a double conversion, superheterodyne, automatic phase tracking receiver, and an X band (8415 MHz) exciter to drive redundant downlink power amplifiers. The receiver acquires and coherently phase tracks the modulated or unmodulated X band (7162 MHz) uplink carrier signal. The exciter phase modulates the band (8415 MHz) downlink signal with composite telemetry and ranging signals. The receiver measured tracking threshold, automatic gain control, static phase error, and phase jitter characteristics of the breadboard DST are in good agreement with the expected performance. The measured results show a receiver tracking threshold of -158 dBm and a dynamic signal range of 88 dB.
Water accessibility in a membrane-inserting peptide comparing Overhauser DNP and pulse EPR methods
DOE Office of Scientific and Technical Information (OSTI.GOV)
Segawa, Takuya F., E-mail: takuya.segawa@alumni.ethz.ch; Doppelbauer, Maximilian; Garbuio, Luca
2016-05-21
Water accessibility is a key parameter for the understanding of the structure of biomolecules, especially membrane proteins. Several experimental techniques based on the combination of electron paramagnetic resonance (EPR) spectroscopy with site-directed spin labeling are currently available. Among those, we compare relaxation time measurements and electron spin echo envelope modulation (ESEEM) experiments using pulse EPR with Overhauser dynamic nuclear polarization (DNP) at X-band frequency and a magnetic field of 0.33 T. Overhauser DNP transfers the electron spin polarization to nuclear spins via cross-relaxation. The change in the intensity of the {sup 1}H NMR spectrum of H{sub 2}O at a Larmormore » frequency of 14 MHz under a continuous-wave microwave irradiation of the nitroxide spin label contains information on the water accessibility of the labeled site. As a model system for a membrane protein, we use the hydrophobic α-helical peptide WALP23 in unilamellar liposomes of DOPC. Water accessibility measurements with all techniques are conducted for eight peptides with different spin label positions and low radical concentrations (10–20 μM). Consistently in all experiments, the water accessibility appears to be very low, even for labels positioned near the end of the helix. The best profile is obtained by Overhauser DNP, which is the only technique that succeeds in discriminating neighboring positions in WALP23. Since the concentration of the spin-labeled peptides varied, we normalized the DNP parameter ϵ, being the relative change of the NMR intensity, by the electron spin concentration, which was determined from a continuous-wave EPR spectrum.« less
Pharmaceutical applications of in vivo EPR
NASA Astrophysics Data System (ADS)
Mäder, Karsten
1998-07-01
The aim of this article is to discuss the applications of in vivo EPR in the field of pharmacy. In addition to direct detection of free radical metabolites and measurement of oxygen, EPR can be used to characterize the mechanisms of drug release from biodegradable polymers. Unique information about drug concentration, the microenvironment (viscosity, polarity, pH) and biodistribution (by localized measurement or EPR Imaging) can be obtained.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Lahoz, F.; Villacampa, B.; Alcala, R.
1997-04-01
The influence of crystal mixing on the structural phase transitions in Rb{sub 1{minus}x}Cs{sub x}CaF{sub 3} (0{lt}x{lt}1) fluoroperovskite crystals has been studied by thermal expansion and EPR measurements of Ni{sup 2+} and Ni{sup 3+} paramagnetic probes. A cubic-to-tetragonal phase transition has been detected in crystals with x=0, 0.1, 0.21, 0.27, and 0.35. The critical temperature and the tetragonal distortion decrease as x increases. No transition was observed for x{ge}0.44. This transition shows a weak first-order component in the x=0 and 0.1 samples, which is progressively smeared out for x{gt}0.1, indicating a spatial distribution of the critical temperature in those crystals withmore » high ionic substitution rate. In RbCaF{sub 3}, another structural phase transition was observed at 20 K with a thermal hysteresis between 20 and 40 K. This transition has not been found in any of the mixed crystals.« less
NASA Astrophysics Data System (ADS)
Haryanto, B.; Bukit, R. Br; Situmeang, E. M.; Christina, E. P.; Pandiangan, F.
2018-02-01
The purpose of this study was to determine the performance, productivity and feasibility of the operation of palm kernel processing plant based on Energy Productivity Ratio (EPR). EPR is expressed as the ratio of output to input energy and by-product. Palm Kernel plan is process in palm kernel to become palm kernel oil. The procedure started from collecting data needed as energy input such as: palm kernel prices, energy demand and depreciation of the factory. The energy output and its by-product comprise the whole production price such as: palm kernel oil price and the remaining products such as shells and pulp price. Calculation the equality of energy of palm kernel oil is to analyze the value of Energy Productivity Ratio (EPR) bases on processing capacity per year. The investigation has been done in Kernel Oil Processing Plant PT-X at Sumatera Utara plantation. The value of EPR was 1.54 (EPR > 1), which indicated that the processing of palm kernel into palm kernel oil is feasible to be operated based on the energy productivity.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Vlieks, Arnold; Dolgashev, Valery; Tantawi, Sami
In support of the MEGa-ray program at LLNL and the High Gradient research program at SLAC, a new X-band multi-cell RF gun is being developed. This gun, similar to earlier guns developed at SLAC for Compton X-ray source program, will be a standing wave structure made of 5.5 cells operating in the pi mode with copper cathode. This gun was designed following criteria used to build SLAC X-band high gradient accelerating structures. It is anticipated that this gun will operate with surface electric fields on the cathode of 200 MeV/m with low breakdown rate. RF will be coupled into themore » structure through a final cell with symmetric duel feeds and with a shape optimized to minimize quadrupole field components. In addition, geometry changes to the original gun, operated with Compton X-ray source, will include a wider RF mode separation, reduced surface electric and magnetic fields.« less
Pulse EPR distance measurements to study multimers and multimerisation
NASA Astrophysics Data System (ADS)
Ackermann, Katrin; Bode, Bela E.
2018-06-01
Pulse dipolar electron paramagnetic resonance (PD-EPR) has become a powerful tool for structural biology determining distances on the nanometre scale. Recent advances in hardware, methodology, and data analysis have widened the scope to complex biological systems. PD-EPR can be applied to systems containing lowly populated conformers or displaying large intrinsic flexibility, making them all but intractable for cryo-electron microscopy and crystallography. Membrane protein applications are of particular interest due to the intrinsic difficulties for obtaining high-resolution structures of all relevant conformations. Many drug targets involved in critical cell functions are multimeric channels or transporters. Here, common approaches for introducing spin labels for PD-EPR cause the presence of more than two electron spins per multimeric complex. This requires careful experimental design to overcome detrimental multi-spin effects and to secure sufficient distance resolution in presence of multiple distances. In addition to obtaining mere distances, PD-EPR can also provide information on multimerisation degrees allowing to study binding equilibria and to determine dissociation constants.
Observations of Heavy Rainfall in a Post Wildland Fire Area Using X-Band Polarimetric Radar
NASA Astrophysics Data System (ADS)
Cifelli, R.; Matrosov, S. Y.; Gochis, D. J.; Kennedy, P.; Moody, J. A.
2011-12-01
Polarimetric X-band radar systems have been used increasingly over the last decade for rainfall measurements. Since X-band radar systems are generally less costly, more mobile, and have narrower beam widths (for same antenna sizes) than those operating at lower frequencies (e.g., C and S-bands), they can be used for the "gap-filling" purposes for the areas when high resolution rainfall measurements are needed and existing operational radars systems lack adequate coverage and/or resolution for accurate quantitative precipitation estimation (QPE). The main drawback of X-band systems is attenuation of radar signals, which is significantly stronger compared to frequencies used by "traditional" precipitation radars operating at lower frequencies. The use of different correction schemes based on polarimetric data can, to a certain degree, overcome this drawback when attenuation does not cause total signal extinction. This presentation will focus on examining the use of high-resolution data from the NOAA Earth System Research Laboratory (ESRL) mobile X-band dual polarimetric radar for the purpose of estimating precipitation in a post-wildland fire area. The NOAA radar was deployed in the summer of 2011 to examine the impact of gap-fill radar on QPE and the resulting hydrologic response during heavy rain events in the Colorado Front Range in collaboration with colleagues from the National Center for Atmospheric Research (NCAR), Colorado State University (CSU), and the U.S. Geological Survey (USGS). A network of rain gauges installed by NCAR, the Denver Urban Drainage Flood Control District (UDFCD), and the USGS are used to compare with the radar estimates. Supplemental data from NEXRAD and the CSU-CHILL dual polarimetric radar are also used to compare with the NOAA X-band and rain gauges. It will be shown that rainfall rates and accumulations estimated from specific differential phase measurements (KDP) at X-band are in good agreement with the measurements from the gauge
Ramos, Paweł; Pieprzyca, Małgorzata; Pilawa, Barbara
2016-01-01
Complex free radical system in thermally sterilized acidum boricum (AB) was studied. Acidum boricum was sterilized at temperatures and times given by pharmaceutical norms: 160 degrees C and 120 min, 170 degrees C and 60 min and 180 degrees C and 30 min. The advanced spectroscopic tests were performed. The EPR spectra of free radicals were measured as the first derivatives with microwaves of 9.3 GHz frequency and magnetic modulation of 100 kHz. The Polish X-band electron paramagnetic resonance spectrometer of Radiopan (Poznań) was used. EPR lines were not observed for the nonheated AB. The broad EPR asymmetric lines were obtained for all the heated AB samples. The influence of microwave power in the range of 2.2-70 mW on the shape of EPR spectra of the heated drug samples was tested. The following asymmetry parameters: A1/A2, A1-A2, B1/B2, and B1-B2, were analyzed. The changes of these parameters with microwave power were observed. The strong dependence of shape and its parameters on microwave power proved the complex character of free radical system in thermally sterilized AB. Changes of microwave power during the detection of EPR spectra indicated complex character of free radicals in AB sterilized in hot air under all the tested conditions. Thermolysis, interactions between free radicals and interactions of free radicals with oxygen may be responsible for the complex free radicals system in thermally treated AB. Usefulness of continuous microwave saturation of EPR lines and shape analysis to examine free radicals in thermally sterilized drugs was confirmed.
Towards band structure and band offset engineering of monolayer Mo(1-x)W(x)S2 via Strain
NASA Astrophysics Data System (ADS)
Kim, Joon-Seok; Ahmad, Rafia; Pandey, Tribhuwan; Rai, Amritesh; Feng, Simin; Yang, Jing; Lin, Zhong; Terrones, Mauricio; Banerjee, Sanjay K.; Singh, Abhishek K.; Akinwande, Deji; Lin, Jung-Fu
2018-01-01
Semiconducting transition metal dichalcogenides (TMDs) demonstrate a wide range of optoelectronic properties due to their diverse elemental compositions, and are promising candidates for next-generation optoelectronics and energy harvesting devices. However, effective band offset engineering is required to implement practical structures with desirable functionalities. Here, we explore the pressure-induced band structure evolution of monolayer WS2 and Mo0.5W0.5S2 using hydrostatic compressive strain applied in a diamond anvil cell (DAC) apparatus and theoretical calculations, in order to study the modulation of band structure and explore the possibility of band alignment engineering through different compositions. Higher W composition in Mo(1-x)W(x)S2 contributes to a greater pressure-sensitivity of direct band gap opening, with a maximum value of 54 meV GPa-1 in WS2. Interestingly, while the conduction band minima (CBMs) remains largely unchanged after the rapid gap increase, valence band maxima (VBMs) significantly rise above the initial values. It is suggested that the pressure- and composition-engineering could introduce a wide variety of band alignments including type I, type II, and type III heterojunctions, and allow to construct precise structures with desirable functionalities. No structural transition is observed during the pressure experiments, implying the pressure could provide selective modulation of band offset.
EPR and Magnetic Susceptibility Studies of Manganese Ions in Bi2O3·CdO Glass Matrix
NASA Astrophysics Data System (ADS)
Ardelean, I.; Todor, Ioana; Ciceo-Lucacel, Raluca; Maniu, Dana
Glasses of the xMnO·(100-x)[Bi2O3·CdO] system with 0
Sutton, Kristin A; Black, Paul J; Mercer, Kermit R; Garman, Elspeth F; Owen, Robin L; Snell, Edward H; Bernhard, William A
2013-12-01
Electron paramagnetic resonance (EPR) and online UV-visible absorption microspectrophotometry with X-ray crystallography have been used in a complementary manner to follow X-ray-induced disulfide-bond cleavage. Online UV-visible spectroscopy showed that upon X-irradiation, disulfide radicalization appeared to saturate at an absorbed dose of approximately 0.5-0.8 MGy, in contrast to the saturating dose of ∼0.2 MGy observed using EPR at much lower dose rates. The observations suggest that a multi-track model involving product formation owing to the interaction of two separate tracks is a valid model for radiation damage in protein crystals. The saturation levels are remarkably consistent given the widely different experimental parameters and the range of total absorbed doses studied. The results indicate that even at the lowest doses used for structural investigations disulfide bonds are already radicalized. Multi-track considerations offer the first step in a comprehensive model of radiation damage that could potentially lead to a combined computational and experimental approach to identifying when damage is likely to be present, to quantitate it and to provide the ability to recover the native unperturbed structure.
Sutton, Kristin A.; Black, Paul J.; Mercer, Kermit R.; Garman, Elspeth F.; Owen, Robin L.; Snell, Edward H.; Bernhard, William A.
2013-01-01
Electron paramagnetic resonance (EPR) and online UV–visible absorption microspectrophotometry with X-ray crystallography have been used in a complementary manner to follow X-ray-induced disulfide-bond cleavage. Online UV–visible spectroscopy showed that upon X-irradiation, disulfide radicalization appeared to saturate at an absorbed dose of approximately 0.5–0.8 MGy, in contrast to the saturating dose of ∼0.2 MGy observed using EPR at much lower dose rates. The observations suggest that a multi-track model involving product formation owing to the interaction of two separate tracks is a valid model for radiation damage in protein crystals. The saturation levels are remarkably consistent given the widely different experimental parameters and the range of total absorbed doses studied. The results indicate that even at the lowest doses used for structural investigations disulfide bonds are already radicalized. Multi-track considerations offer the first step in a comprehensive model of radiation damage that could potentially lead to a combined computational and experimental approach to identifying when damage is likely to be present, to quantitate it and to provide the ability to recover the native unperturbed structure. PMID:24311579
Locations of radical species in black pepper seeds investigated by CW EPR and 9 GHz EPR imaging
NASA Astrophysics Data System (ADS)
Nakagawa, Kouichi; Epel, Boris
2014-10-01
In this study, noninvasive 9 GHz electron paramagnetic resonance (EPR)-imaging and continuous wave (CW) EPR were used to investigate the locations of paramagnetic species in black pepper seeds without further irradiation. First, lithium phthalocyanine (LiPC) phantom was used to examine 9 GHz EPR imaging capabilities. The 9 GHz EPR-imager easily resolved the LiPC samples at a distance of ∼2 mm. Then, commercially available black pepper seeds were measured. We observed signatures from three different radical species, which were assigned to stable organic radicals, Fe3+, and Mn2+ complexes. In addition, no EPR spectral change in the seed was observed after it was submerged in distilled H2O for 1 h. The EPR and spectral-spatial EPR imaging results suggested that the three paramagnetic species were mostly located at the seed surface. Fewer radicals were found inside the seed. We demonstrated that the CW EPR and 9 GHz EPR imaging were useful for the determination of the spatial distribution of paramagnetic species in various seeds.
Locations of radical species in black pepper seeds investigated by CW EPR and 9GHz EPR imaging.
Nakagawa, Kouichi; Epel, Boris
2014-10-15
In this study, noninvasive 9GHz electron paramagnetic resonance (EPR)-imaging and continuous wave (CW) EPR were used to investigate the locations of paramagnetic species in black pepper seeds without further irradiation. First, lithium phthalocyanine (LiPC) phantom was used to examine 9GHz EPR imaging capabilities. The 9GHz EPR-imager easily resolved the LiPC samples at a distance of ∼2mm. Then, commercially available black pepper seeds were measured. We observed signatures from three different radical species, which were assigned to stable organic radicals, Fe(3+), and Mn(2+) complexes. In addition, no EPR spectral change in the seed was observed after it was submerged in distilled H2O for 1h. The EPR and spectral-spatial EPR imaging results suggested that the three paramagnetic species were mostly located at the seed surface. Fewer radicals were found inside the seed. We demonstrated that the CW EPR and 9GHz EPR imaging were useful for the determination of the spatial distribution of paramagnetic species in various seeds. Copyright © 2014 Elsevier B.V. All rights reserved.
NASA Astrophysics Data System (ADS)
Lahoz, F.; Villacampa, B.; Alcalá, R.; Marquina, C.; Ibarra, M. R.
1997-04-01
The influence of crystal mixing on the structural phase transitions in Rb1-xCsxCaF3 (0<x<1) fluoroperovskite crystals has been studied by thermal expansion and EPR measurements of Ni2+ and Ni3+ paramagnetic probes. A cubic-to-tetragonal phase transition has been detected in crystals with x=0, 0.1, 0.21, 0.27, and 0.35. The critical temperature and the tetragonal distortion decrease as x increases. No transition was observed for x>=0.44. This transition shows a weak first-order component in the x=0 and 0.1 samples, which is progressively smeared out for x>0.1, indicating a spatial distribution of the critical temperature in those crystals with high ionic substitution rate. In RbCaF3 , another structural phase transition was observed at 20 K with a thermal hysteresis between 20 and 40 K. This transition has not been found in any of the mixed crystals.
X-SAR: The X-band synthetic aperture radar on board the Space Shuttle
NASA Technical Reports Server (NTRS)
Werner, Marian U.
1993-01-01
The X-band synthetic aperture radar (X-SAR) is the German/Italian contribution to the NASA/JPL Shuttle Radar Lab missions as part of the preparation for the Earth Observation System (EOS) program. The Shuttle Radar Lab is a combination of several radars: an L-band (1.2 GHz) and a C-band (5.3 GHz) multipolarization SAR known as SIR-C (Shuttle Imaging Radar); and an X-band (9.6 GHz) vertically polarized SAR which will be operated synchronously over the same target areas to deliver calibrated multifrequency and multipolarization SAR data at multiple incidence angles from space. A joint German/Italian project office at DARA (German Space Agency) is responsible for the management of the X-SAR project. The space hardware has been developed and manufactured under industrial contract by Dornier and Alenia Spazio. Besides supporting all the technical and scientific tasks, DLR, in cooperation with ASI (Agencia Spaziale Italiano) is responsible for mission operation, calibration, and high precision SAR processing. In addition, DLR developed an airborne X-band SAR to support the experimenters with campaigns to prepare for the missions. The main advantage of adding a shorter wavelength (3 cm) radar to the SIR-C radars is the X-band radar's weaker penetration into vegetation and soil and its high sensitivity to surface roughness and associated phenomena. The performance of each of the three radars is comparable with respect to radiometric and geometric resolution.
Vasco, D. W.; Rutqvist, Jonny; Ferretti, Alessandro; ...
2013-06-07
In this study, we resolve deformation at The Geysers Geothermal Field using two distinct sets of interferometric synthetic aperture radar (InSAR) data. The first set of observations utilize archived European Space Agency C-band synthetic aperture radar data from 1992 through 1999 to image the long-term and large-scale subsidence at The Geysers. The peak range velocity of approximately 50 mm/year agrees with previous estimates from leveling and global positioning system observations. Data from a second set of measurements, acquired by TerraSAR-X satellites, extend from May 2011 until April 2012 and overlap the C-band data spatially but not temporally. These X-band data,more » analyzed using a combined permanent and distributed scatterer algorithm, provide a higher density of scatterers (1122 per square kilometer) than do the C-band data (12 per square kilometer). The TerraSAR-X observations resolve 1 to 2 cm of deformation due to water injection into a Northwest Geysers enhanced geothermal system well, initiated on October 2011. Lastly, the temporal variation of the deformation is compatible with estimates from coupled numerical modeling.« less
Chodurek, Ewa; Zdybel, Magdalena; Pilawa, Barbara; Dzierzewicz, Zofia
2012-01-01
Drug binding by melanin biopolymers influence the effectiveness of the chemotherapy, radiotherapy and photodynamic therapy. Free radicals of melanins take part in formation of their complex with drugs. The aim of this work was to determine the effect of the two compounds: valproic acid (VPA) and cisplatin (CPT) on free radicals properties of melanin isolated from A-375 melanoma cells. Free radicals were examined by an X-band (9.3 GHz) electron paramagnetic resonance (EPR) spectroscopy. EPR spectra were measured for the model synthetic eumelanin - DOPA-melanin, the melanin isolated from the control A-375 cells and these cells treated by VPA, CPT and both VPA and CPT. For all the examined samples broad EPR lines (deltaBpp: 0.48-0.68 mT) with g-factors of 2.0045-2.0060 characteristic for o-semiquinone free radicals were observed. Free radicals concentrations (N) in the tested samples, g-factors, amplitudes (A), integral intensities (I) and linewidths (deltaBpp) of the EPR spectra, were analyzed. The EPR lines were homogeneously broadened. Continuous microwave saturation of the EPR spectra indicated that slow spin-lattice relaxation processes existed in all the tested melanin samples. The relatively slowest spin-lattice relaxation processes characterized melanin isolated from A-375 cells treated with both VPA and CPT. The changes of the EPR spectra with increasing microwave power in the range of 2.2-70 mW were evaluated. Free radicals concentrations in the melanin from A-375 cells were higher than in the synthetic DOPA-melanin. The strong increase of free radicals concentration in the melanin from A-375 cells was observed after their treating by VPA. CPT also caused the increase of free radicals concentrations in the examined natural melanin. The free radicals concentration in melanin isolated from A-375 cells treated with both VPA and CPT was slightly higher than those in melanin from the control cells.
Density Measurements in Air by Optically Exciting the Cordes Bands of I2
NASA Technical Reports Server (NTRS)
Balla, R. Jeffrey; Exton, Reginald J.
2000-01-01
We describe an optical method based on laser-induced fluorescence for obtaining instantaneous measurements of density along a line in low-density air seeded with I2. The Cordes bands of I2 (D(sup 1)sigma(sup +, sub u)) left arrow X(sup 1)sigma(sup +, sub g)) are excited with a tunable ArF excimer laser. air densities in the range (0.1-6.5) x 10(exp 17) cm(exp -3) are measured over 295-583 K using the density-dependent emission ratio of two emission bands of I2; the 340 nm bands and the diffuse-structured McLennan bands near 320 nm.
EPR, optical absorption and luminescence studies of Cr3+-doped antimony phosphate glasses
NASA Astrophysics Data System (ADS)
De Vicente, F. S.; Santos, F. A.; Simões, B. S.; Dias, S. T.; Siu Li, M.
2014-12-01
Antimony phosphate glasses (SbPO) doped with 3 and 6 mol% of Cr3+ were studied by Electron Paramagnetic Resonance (EPR), UV-VIS optical absorption and luminescence spectroscopy. The EPR spectra of Cr3+-doped glasses showed two principal resonance signals with effective g values at g = 5.11 and g = 1.97. UV-VIS optical absorption spectra of SbPO:Cr3+ presented four characteristics bands at 457, 641, 675, and 705 nm related to the transitions from 4A2(F) to 4T1(F), 4T2(F), 2T1(G), and 2E(G), respectively, of Cr3+ ions in octahedral symmetry. Optical absorption spectra of SbPO:Cr3+ allowed evaluating the crystalline field Dq, Racah parameters (B and C) and Dq/B. The calculated value of Dq/B = 2.48 indicates that Cr3+ ions in SbPO glasses are in strong ligand field sites. The optical band gap for SbPO and SbPO:Cr3+ were evaluated from the UV optical absorption edges. Luminescence measurements of pure and Cr3+-doped glasses excited with 350 nm revealed weak emission bands from 400 to 600 nm due to the 3P1 → 1S0 electronic transition from Sb3+ ions. Cr3+-doped glasses excited with 415 nm presented Cr3+ characteristic luminescence spectra composed by two broad bands, one band centered at 645 nm (2E → 4A2) and another intense band from 700 to 850 nm (4T2 → 4A2).
One-way EPR steering and genuine multipartite EPR steering
NASA Astrophysics Data System (ADS)
He, Qiongyi; Reid, Margaret D.
2012-11-01
We propose criteria and experimental strategies to realise the Einstein-Podolsky-Rosen (EPR) steering nonlocality. One-way steering can be obtained where there is asymmetry of thermal noise on each system. We also present EPR steering inequalities that act as signatures and suggest how to optimise EPR correlations in specific schemes so that the genuine multipartite EPR steering nonlocality (EPR paradox) can also possibly be realised. The results presented here also apply to the spatially separated macroscopic atomic ensembles.
Impurity-Band Model for GaP1-xNx
DOE Office of Scientific and Technical Information (OSTI.GOV)
Fluegel, B.; Zhang, Y.; Geisz, J. F.
2005-11-01
Low-temperature absorption studies on free-standing GaP1-xNx films provide direct experimental evidence that the host conduction-band minimum (CBM) near X1C does not plunge downward with increased nitrogen doping, contrary to what has been suggested recently; rather, it remains stationary for x up to 0.1%. This fact, combined with the results of earlier studies of the CBM at ..GAMMA.. and conduction-band edge near L, confirms that the giant bandgap lowering observed in GaP1-xNx results from a CBM that evolves purely from nitrogen impurity bands.
Estimating tropical forest structure using LIDAR AND X-BAND INSAR
NASA Astrophysics Data System (ADS)
Palace, M. W.; Treuhaft, R. N.; Keller, M. M.; Sullivan, F.; Roberto dos Santos, J.; Goncalves, F. G.; Shimbo, J.; Neumann, M.; Madsen, S. N.; Hensley, S.
2013-12-01
Tropical forests are considered the most structurally complex of all forests and are experiencing rapid change due to anthropogenic and climatic factors. The high carbon stocks and fluxes make understanding tropical forests highly important to both regional and global studies involving ecosystems and climate. Large and remote areas in the tropics are prime targets for the use of remotely sensed data. Radar and lidar have previously been used to estimate forest structure, with an emphasis on biomass. These two remote sensing methods have the potential to yield much more information about forest structure, specifically through the use of X-band radar and waveform lidar data. We examined forest structure using both field-based and remotely sensed data in the Tapajos National Forest, Para, Brazil. We measured multiple structural parameters for about 70 plots in the field within a 25 x 15 km area that have TanDEM-X single-pass horizontally and vertically polarized radar interferometric data. High resolution airborne lidar were collected over a 22 sq km portion of the same area, within which 33 plots were co-located. Preliminary analyses suggest that X-band interferometric coherence decreases by about a factor of 2 (from 0.95 to 0.45) with increasing field-measured vertical extent (average heights of 7-25 m) and biomass (10-430 Mg/ha) for a vertical wavelength of 39 m, further suggesting, as has been observed at C-band, that interferometric synthetic aperture radar (InSAR) is substantially more sensitive to forest structure/biomass than SAR. Unlike InSAR coherence versus biomass, SAR power at X-band versus biomass shows no trend. Moreover, airborne lidar coherence at the same vertical wavenumbers as InSAR is also shown to decrease as a function of biomass, as well. Although the lidar coherence decrease is about 15% more than the InSAR, implying that lidar penetrates more than InSAR, these preliminary results suggest that X-band InSAR may be useful for structure and
NASA Technical Reports Server (NTRS)
Morabito, D. D.
2002-01-01
Simultaneous dual-frequency Ka-band (32 GHz) and X-band (8.4 GHz) carrier signal data have been acquired during the superior conjunction of the Cassini spacecraft June 2001, using the NASA Deep Space Network's facilities located in Goldstone, California. The solar elongation angle of the observations varied from -4.1 degrees (-16 solar radii) to -0.6 degrees (-2.3 solar radii). The observed coronal and solar effects on the signals include spectral broadening, amplitude scintillation, phase scintillation, and increased noise. The measurements were generally consistent with existing solar models, except during solar transient events when the signatures of the measurements were observed to increase significantly above the quiet background levels. This is the second solar conjunction of Cassini for which simultaneous X/Ka data were acquired. Both solar conjunctions, conducted in May 2000 and June 2001, occurred near the peak of the current 11 year solar cycle.
Quantitative analysis of dinuclear manganese(II) EPR spectra
NASA Astrophysics Data System (ADS)
Golombek, Adina P.; Hendrich, Michael P.
2003-11-01
A quantitative method for the analysis of EPR spectra from dinuclear Mn(II) complexes is presented. The complex [(Me 3TACN) 2Mn(II) 2(μ-OAc) 3]BPh 4 ( 1) (Me 3TACN= N, N', N''-trimethyl-1,4,7-triazacyclononane; OAc=acetate 1-; BPh 4=tetraphenylborate 1-) was studied with EPR spectroscopy at X- and Q-band frequencies, for both perpendicular and parallel polarizations of the microwave field, and with variable temperature (2-50 K). Complex 1 is an antiferromagnetically coupled dimer which shows signals from all excited spin manifolds, S=1 to 5. The spectra were simulated with diagonalization of the full spin Hamiltonian which includes the Zeeman and zero-field splittings of the individual manganese sites within the dimer, the exchange and dipolar coupling between the two manganese sites of the dimer, and the nuclear hyperfine coupling for each manganese ion. All possible transitions for all spin manifolds were simulated, with the intensities determined from the calculated probability of each transition. In addition, the non-uniform broadening of all resonances was quantitatively predicted using a lineshape model based on D- and r-strain. As the temperature is increased from 2 K, an 11-line hyperfine pattern characteristic of dinuclear Mn(II) is first observed from the S=3 manifold. D- and r-strain are the dominate broadening effects that determine where the hyperfine pattern will be resolved. A single unique parameter set was found to simulate all spectra arising for all temperatures, microwave frequencies, and microwave modes. The simulations are quantitative, allowing for the first time the determination of species concentrations directly from EPR spectra. Thus, this work describes the first method for the quantitative characterization of EPR spectra of dinuclear manganese centers in model complexes and proteins. The exchange coupling parameter J for complex 1 was determined ( J=-1.5±0.3 cm-1; H ex=-2J S1· S2) and found to be in agreement with a previous
2016-01-01
This work demonstrates the feasibility of making sensitive nanometer distance measurements between Fe(III) heme centers and nitroxide spin labels in proteins using the double electron–electron resonance (DEER) pulsed EPR technique at 94 GHz. Techniques to measure accurately long distances in many classes of heme proteins using DEER are currently strongly limited by sensitivity. In this paper we demonstrate sensitivity gains of more than 30 times compared with previous lower frequency (X-band) DEER measurements on both human neuroglobin and sperm whale myoglobin. This is achieved by taking advantage of recent instrumental advances, employing wideband excitation techniques based on composite pulses and exploiting more favorable relaxation properties of low-spin Fe(III) in high magnetic fields. This gain in sensitivity potentially allows the DEER technique to be routinely used as a sensitive probe of structure and conformation in the large number of heme and many other metalloproteins. PMID:27035368
Experimental EPR-steering using Bell-local states
NASA Astrophysics Data System (ADS)
Saunders, D. J.; Jones, S. J.; Wiseman, H. M.; Pryde, G. J.
2010-11-01
The concept of `steering' was introduced in 1935 by Schrödinger as a generalization of the EPR (Einstein-Podolsky-Rosen) paradox. It has recently been formalized as a quantum-information task with arbitrary bipartite states and measurements, for which the existence of entanglement is necessary but not sufficient. Previous experiments in this area have been restricted to an approach that followed the original EPR argument in considering only two different measurement settings per side. Here we demonstrate experimentally that EPR-steering occurs for mixed entangled states that are Bell local (that is, that cannot possibly demonstrate Bell non-locality). Unlike the case of Bell inequalities, increasing the number of measurement settings beyond two-we use up to six-significantly increases the robustness of the EPR-steering phenomenon to noise.
EPR and IR spectral investigations on some leafy vegetables of Indian origin
NASA Astrophysics Data System (ADS)
Prasuna, C. P. Lakshmi; Chakradhar, R. P. S.; Rao, J. L.; Gopal, N. O.
2009-09-01
EPR spectral investigations have been carried out on four edible leafy vegetables of India, which are used as dietary component in day to day life. In Rumex vesicarius leaf sample, EPR spectral investigations at different temperatures indicate the presence of anti-ferromagnetically coupled Mn(IV)-Mn(IV) complexes. EPR spectra of Trigonella foenum graecum show the presence of Mn ions in multivalent state and Fe 3+ ions in rhombic symmetry. EPR spectra of Basella rubra indicate the presence of Mn(IV)-O-Mn(IV) type complexes. The EPR spectra of Basella rubra have been studied at different temperatures. It is found that the spin population for the resonance signal at g = 2.06 obeys the Boltzmann distribution law. The EPR spectra of Moringa oliefera leaves show the presence of Mn 2+ ions. Radiation induced changes in free radical of this sample have also been studied. The FT-IR spectra of Basella rubra and Moringa oliefera leaves show the evidences for the protein matrix bands and those corresponding to carboxylic C dbnd O bonds.
Nitrogen-Induced Perturbation of the Valence Band States in GaP1-xNx Alloys
DOE Office of Scientific and Technical Information (OSTI.GOV)
Dudiy, S. V.; Zunger, A.; Felici, M.
2006-01-01
The effects of diluted nitrogen impurities on the valence- and conduction-band states of GaP{sub 1-x}N{sub x} have been predicted and measured experimentally. The calculation uses state-of-the-art atomistic modeling: we use large supercells with screened pseudopotentials and consider several random realizations of the nitrogen configurations. These calculations agree with photoluminescence excitation (PLE) measurements performed for nitrogen concentrations x up to 0.035 and photon energies up to 1 eV above the GaP optical-absorption edge, as well as with published ellipsometry data. In particular, a predicted nitrogen-induced buildup of the L character near the valence- and conduction-band edges accounts for the surprising broad-absorptionmore » plateau observed in PLE between the X{sub 1c} and the {Lambda}{sub 1c} critical points of GaP. Moreover, theory accounts quantitatively for the downward bowing of the indirect conduction-band edge and for the upward bowing of the direct transition with increasing nitrogen concentration. We review some of the controversies in the literature regarding the shifts in the conduction band with composition, and conclude that measured results at ultralow N concentration cannot be used to judge behavior at a higher concentration. In particular, we find that at the high concentrations of nitrogen studied here ({approx}1%) the conduction-band edge (CBE) is a hybridized state made from the original GaP X{sub 1c} band-edge state plus all cluster states. In this limit, the CBE plunges down in energy as the N concentration increases, in quantitative agreement with the measurements reported here. However, at ultralow nitrogen concentrations (<0.1%), the CBE is the nearly unperturbed host X{sub 1c}, which does not sense the nitrogen cluster levels. Thus, this state does not move energetically as nitrogen is added and stays pinned in energy, in agreement with experimental results.« less
X-band RF gun and linac for medical Compton scattering X-ray source
NASA Astrophysics Data System (ADS)
Dobashi, Katsuhito; Uesaka, Mitsuru; Fukasawa, Atsushi; Sakamoto, Fumito; Ebina, Futaro; Ogino, Haruyuki; Urakawa, Junji; Higo, Toshiyasu; Akemoto, Mitsuo; Hayano, Hitoshi; Nakagawa, Keiichi
2004-12-01
Compton scattering hard X-ray source for 10-80 keV are under construction using the X-band (11.424 GHz) electron linear accelerator and YAG laser at Nuclear Engineering Research laboratory, University of Tokyo. This work is a part of the national project on the development of advanced compact medical accelerators in Japan. National Institute for Radiological Science is the host institute and U.Tokyo and KEK are working for the X-ray source. Main advantage is to produce tunable monochromatic hard (10-80 keV) X-rays with the intensities of 108-1010 photons/s (at several stages) and the table-top size. Second important aspect is to reduce noise radiation at a beam dump by adopting the deceleration of electrons after the Compton scattering. This realizes one beamline of a 3rd generation SR source at small facilities without heavy shielding. The final goal is that the linac and laser are installed on the moving gantry. We have designed the X-band (11.424 GHz) traveling-wave-type linac for the purpose. Numerical consideration by CAIN code and luminosity calculation are performed to estimate the X-ray yield. X-band thermionic-cathode RF-gun and RDS(Round Detuned Structure)-type X-band accelerating structure are applied to generate 50 MeV electron beam with 20 pC microbunches (104) for 1 microsecond RF macro-pulse. The X-ray yield by the electron beam and Q-switch Nd:YAG laser of 2 J/10 ns is 107 photons/RF-pulse (108 photons/sec at 10 pps). We design to adopt a technique of laser circulation to increase the X-ray yield up to 109 photons/pulse (1010 photons/s). 50 MW X-band klystron and compact modulator have been constructed and now under tuning. The construction of the whole system has started. X-ray generation and medical application will be performed in the early next year.
Tunable band gap in Bi(Fe1-xMnx)O3 films
NASA Astrophysics Data System (ADS)
Xu, X. S.; Ihlefeld, J. F.; Lee, J. H.; Ezekoye, O. K.; Vlahos, E.; Ramesh, R.; Gopalan, V.; Pan, X. Q.; Schlom, D. G.; Musfeldt, J. L.
2010-05-01
In order to investigate band gap tunability in polar oxides, we measured the optical properties of a series of Bi(Fe1-xMnx)O3 thin films. The absorption response of the mixed metal solid solutions is approximately a linear combination of the characteristics of the two end members, a result that demonstrates straightforward band gap tunability in this system.
X/X/Ka-band prime focus feed antenna for the Mars Observer beacon spacecraft
NASA Technical Reports Server (NTRS)
Stanton, P.; Reilly, H.; Esquivel, M.
1988-01-01
The results of an X/X/Ka-band feed design concept demonstration are presented. The purpose is to show the feasibility of adding a Ka-band beacon to the Mars Observer spacecraft. Scale model radiation patterns were made and analyzed.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Fluegel, B.; Mascarenhas, A.; Ptak, A. J.
2007-01-01
An above-band-gap transition E{sub +} is experimentally observed in the dilute GaAs{sub 1-x}Bi{sub x} alloy. Precise measurements at very low dilutions are made of the above-band-gap transition E{sub +} that is observed in GaAs{sub 1-x}N{sub x}, making it possible to compare the behavior of the different isoelectronic traps Bi and N in the common host GaAs with respect to their perturbation to the host electronic structure. We suggest that the origin of the E{sub +} level observed in GaAs is not the isolated isoelectronic impurity level N{sub x}, as is presumed in the band-anticrossing model, but rather the isoelectronic-impurity-induced perturbationmore » of the conduction band L{sub 6}{sup c}.« less
Standard Observing Bands: Is Now the Time to Replace S/X with X/Ka?
NASA Technical Reports Server (NTRS)
Jacobs, C. S.; Lanyi, G. E.; Naudet, C. J.
2004-01-01
In this paper we will argue that the VLBI community should be developing a road map to transition from S/X to simultaneous X and Ka-band (32 GHz) observations. There are both negative and positive reasons for planning such a transition. On the negative side, we will outline concerns that S-band observations may be headed toward obsolescence. On the positive side, we will refer to evidence that X/Ka has potential for providing a more stable reference frame than S/X. We will propose timetables for a transition to X/Ka observing starting from the current status of X/Ka and plans that are now taking shape. First X/Ka fringes were obtained in 2001 with the Deep Space Network. Future plans will be discussed including a proposed X/Ka-band upgrade to the VLBA. Lastly, we will consider the need for a period of overlap between S/X and X/Ka so that the long and rich history of astrometric and geodetic VLBI is not compromised.
NASA Technical Reports Server (NTRS)
Mysoor, N. R.; Perret, J. D.; Kermode, A. W.
1991-01-01
The design concepts and measured performance characteristics are summarized of an X band (7162 MHz/8415 MHz) breadboard deep space transponder (DSP) for future spacecraft applications, with the first use scheduled for the Comet Rendezvous Asteroid Flyby (CRAF) and Cassini missions in 1995 and 1996, respectively. The DST consists of a double conversion, superheterodyne, automatic phase tracking receiver, and an X band (8415 MHz) exciter to drive redundant downlink power amplifiers. The receiver acquires and coherently phase tracks the modulated or unmodulated X band (7162 MHz) uplink carrier signal. The exciter phase modulates the X band (8415 MHz) downlink signal with composite telemetry and ranging signals. The receiver measured tracking threshold, automatic gain control, static phase error, and phase jitter characteristics of the breadboard DST are in good agreement with the expected performance. The measured results show a receiver tracking threshold of -158 dBm and a dynamic signal range of 88 dB.
Digitally generated excitation and near-baseband quadrature detection of rapid scan EPR signals.
Tseitlin, Mark; Yu, Zhelin; Quine, Richard W; Rinard, George A; Eaton, Sandra S; Eaton, Gareth R
2014-12-01
The use of multiple synchronized outputs from an arbitrary waveform generator (AWG) provides the opportunity to perform EPR experiments differently than by conventional EPR. We report a method for reconstructing the quadrature EPR spectrum from periodic signals that are generated with sinusoidal magnetic field modulation such as continuous wave (CW), multiharmonic, or rapid scan experiments. The signal is down-converted to an intermediate frequency (IF) that is less than the field scan or field modulation frequency and then digitized in a single channel. This method permits use of a high-pass analog filter before digitization to remove the strong non-EPR signal at the IF, that might otherwise overwhelm the digitizer. The IF is the difference between two synchronized X-band outputs from a Tektronix AWG 70002A, one of which is for excitation and the other is the reference for down-conversion. To permit signal averaging, timing was selected to give an exact integer number of full cycles for each frequency. In the experiments reported here the IF was 5kHz and the scan frequency was 40kHz. To produce sinusoidal rapid scans with a scan frequency eight times IF, a third synchronized output generated a square wave that was converted to a sine wave. The timing of the data acquisition with a Bruker SpecJet II was synchronized by an external clock signal from the AWG. The baseband quadrature signal in the frequency domain was reconstructed. This approach has the advantages that (i) the non-EPR response at the carrier frequency is eliminated, (ii) both real and imaginary EPR signals are reconstructed from a single physical channel to produce an ideal quadrature signal, and (iii) signal bandwidth does not increase relative to baseband detection. Spectra were obtained by deconvolution of the reconstructed signals for solid BDPA (1,3-bisdiphenylene-2-phenylallyl) in air, 0.2mM trityl OX63 in water, 15 N perdeuterated tempone, and a nitroxide with a 0.5G partially-resolved proton
NASA Technical Reports Server (NTRS)
Manshadi, F.
1986-01-01
A low-loss bandstop filter designed and developed for the Deep Space Network's 34-meter high-efficiency antennas is described. The filter is used for protection of the X-band traveling wave masers from the 20-kW transmitter signal. A combination of empirical and theoretical techniques was employed as well as computer simulation to verify the design before fabrication.
BCL::MP-Fold: membrane protein structure prediction guided by EPR restraints
Fischer, Axel W.; Alexander, Nathan S.; Woetzel, Nils; Karakaş, Mert; Weiner, Brian E.; Meiler, Jens
2016-01-01
For many membrane proteins, the determination of their topology remains a challenge for methods like X-ray crystallography and nuclear magnetic resonance (NMR) spectroscopy. Electron paramagnetic resonance (EPR) spectroscopy has evolved as an alternative technique to study structure and dynamics of membrane proteins. The present study demonstrates the feasibility of membrane protein topology determination using limited EPR distance and accessibility measurements. The BCL::MP-Fold algorithm assembles secondary structure elements (SSEs) in the membrane using a Monte Carlo Metropolis (MCM) approach. Sampled models are evaluated using knowledge-based potential functions and agreement with the EPR data and a knowledge-based energy function. Twenty-nine membrane proteins of up to 696 residues are used to test the algorithm. The protein-size-normalized root-mean-square-deviation (RMSD100) value of the most accurate model is better than 8 Å for twenty-seven, better than 6 Å for twenty-two, and better than 4 Å for fifteen out of twenty-nine proteins, demonstrating the algorithm’s ability to sample the native topology. The average enrichment could be improved from 1.3 to 2.5, showing the improved discrimination power by using EPR data. PMID:25820805
Niedermeier, Christian A.; Råsander, Mikael; Rhode, Sneha; Kachkanov, Vyacheslav; Zou, Bin; Alford, Neil; Moram, Michelle A.
2016-01-01
Epitaxial transparent oxide NixMg1−xO (0 ≤ x ≤ 1) thin films were grown on MgO(100) substrates by pulsed laser deposition. High-resolution synchrotron X-ray diffraction and high-resolution transmission electron microscopy analysis indicate that the thin films are compositionally and structurally homogeneous, forming a completely miscible solid solution. Nevertheless, the composition dependence of the NixMg1−xO optical band gap shows a strong non-parabolic bowing with a discontinuity at dilute NiO concentrations of x < 0.037. Density functional calculations of the NixMg1−xO band structure and the density of states demonstrate that deep Ni 3d levels are introduced into the MgO band gap, which significantly reduce the fundamental gap as confirmed by optical absorption spectra. These states broaden into a Ni 3d-derived conduction band for x > 0.074 and account for the anomalously large band gap narrowing in the NixMg1−xO solid solution system. PMID:27503808
X-ray and EPR Characterization of the Auxiliary Fe-S Clusters in the Radical SAM Enzyme PqqE.
Barr, Ian; Stich, Troy A; Gizzi, Anthony S; Grove, Tyler L; Bonanno, Jeffrey B; Latham, John A; Chung, Tyler; Wilmot, Carrie M; Britt, R David; Almo, Steven C; Klinman, Judith P
2018-02-27
The Radical SAM (RS) enzyme PqqE catalyzes the first step in the biosynthesis of the bacterial cofactor pyrroloquinoline quinone, forming a new carbon-carbon bond between two side chains within the ribosomally synthesized peptide substrate PqqA. In addition to the active site RS 4Fe-4S cluster, PqqE is predicted to have two auxiliary Fe-S clusters, like the other members of the SPASM domain family. Here we identify these sites and examine their structure using a combination of X-ray crystallography and Mössbauer and electron paramagnetic resonance (EPR) spectroscopies. X-ray crystallography allows us to identify the ligands to each of the two auxiliary clusters at the C-terminal region of the protein. The auxiliary cluster nearest the RS site (AuxI) is in the form of a 2Fe-2S cluster ligated by four cysteines, an Fe-S center not seen previously in other SPASM domain proteins; this assignment is further supported by Mössbauer and EPR spectroscopies. The second, more remote cluster (AuxII) is a 4Fe-4S center that is ligated by three cysteine residues and one aspartate residue. In addition, we examined the roles these ligands play in catalysis by the RS and AuxII clusters using site-directed mutagenesis coupled with EPR spectroscopy. Lastly, we discuss the possible functional consequences that these unique AuxI and AuxII clusters may have in catalysis for PqqE and how these may extend to additional RS enzymes catalyzing the post-translational modification of ribosomally encoded peptides.
Contribution of Harold M. Swartz to In Vivo EPR and EPR Dosimetry.
Gallez, Bernard
2016-12-01
In 2015, we are celebrating half a century of research in the application of Electron Paramagnetic Resonance (EPR) as a biodosimetry tool to evaluate the dose received by irradiated people. During the EPR Biodose 2015 meeting, a special session was organized to acknowledge the pioneering contribution of Harold M. (Hal) Swartz in the field. The article summarizes his main contribution in physiology and medicine. Four emerging themes have been pursued continuously along his career since its beginning: (1) radiation biology; (2) oxygen and oxidation; (3) measuring physiology in vivo; and (4) application of these measurements in clinical medicine. The common feature among all these different subjects has been the use of magnetic resonance techniques, especially EPR. In this article, you will find an impressionist portrait of Hal Swartz with the description of the 'making of' this pioneer, a time-line perspective on his career with the creation of three National Institutes of Health-funded EPR centers, a topic-oriented perspective on his career with a description of his major contributions to Science, his role as a mentor and his influence on his academic children, his active role as founder of scientific societies and organizer of scientific meetings, and the well-deserved international recognition received so far. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.
High-field/ high-frequency EPR study on stable free radicals formed in sucrose by gamma-irradiation.
Georgieva, Elka R; Pardi, Luca; Jeschke, Gunnar; Gatteschi, Dante; Sorace, Lorenzo; Yordanov, Nicola D
2006-06-01
The EPR spectrum of sucrose irradiated by high-energy radiation is complex due to the presence of more than one radical species. In order to decompose the spectrum and elucidate the radical magnetic parameters a high-field (HF(-)EPR) study on stable free radicals in gamma-irradiated polycrystalline sucrose (table sugar) was performed at three different high frequencies--94, 190 and 285 GHz as well as at the conventional X-band. We suggest a presence of three stable radicals R1, R2 and R3 as the main radical species. Due to the increase of g-factor resolution at high fields the g-tensors of these radicals could be extracted by accurate simulations. The moderate g-anisotropy suggests that all three radicals are carbon-centred. Results from an earlier ENDOR study on X-irradiated sucrose single crystals (Vanhaelewyn et al., Appl Radiat Isot, 52, 1221 (2000)) were used for analyzing of the spectra in more details. It was confirmed that the strongest hyperfine interaction has a relatively small anisotropy, which indicates either the absence of alpha-protons or a strongly distorted geometry of the radicals.
Mainali, Laxman; Vasquez-Vivar, Jeannette; Hyde, James S.; Subczynski, Witold K.
2015-01-01
This study validated the use of small unilamellar vesicles (SUVs) made of 1-palmitoyl-2-oleoylphosphatidylcholine with 1 mol% spin label of 1-palmitoyl-2-(16-doxylstearoyl)phosphatidylcholine (16-PC) as an oxygen sensitive analyte to study cellular respiration. In the analyte the hydrocarbon environment surrounds the nitroxide moiety of 16-PC. This ensures high oxygen concentration and oxygen diffusion at the location of the nitroxide as well as isolation of the nitroxide moiety from cellular reductants and paramagnetic ions that might interfere with spin-label oximetry measurements. The saturation-recovery EPR approach was applied in the analysis since this approach is the most direct method to carry out oximetric studies. It was shown that this display (spin-lattice relaxation rate) is linear in oxygen partial pressure up to 100% air (159 mmHg). Experiments using a neuronal cell line in suspension were carried out at X-band for closed chamber geometry. Oxygen consumption rates showed a linear dependence on the number of cells. Other significant benefits of the analyte are: the fast effective rotational diffusion and slow translational diffusion of the spin-probe is favorable for the measurements, and there is no cross reactivity between oxygen and paramagnetic ions in the lipid bilayer. PMID:26441482
Mainali, Laxman; Vasquez-Vivar, Jeannette; Hyde, James S; Subczynski, Witold K
2015-08-01
This study validated the use of small unilamellar vesicles (SUVs) made of 1-palmitoyl-2-oleoylphosphatidylcholine with 1 mol% spin label of 1-palmitoyl-2-(16-doxylstearoyl)phosphatidylcholine (16-PC) as an oxygen sensitive analyte to study cellular respiration. In the analyte the hydrocarbon environment surrounds the nitroxide moiety of 16-PC. This ensures high oxygen concentration and oxygen diffusion at the location of the nitroxide as well as isolation of the nitroxide moiety from cellular reductants and paramagnetic ions that might interfere with spin-label oximetry measurements. The saturation-recovery EPR approach was applied in the analysis since this approach is the most direct method to carry out oximetric studies. It was shown that this display (spin-lattice relaxation rate) is linear in oxygen partial pressure up to 100% air (159 mmHg). Experiments using a neuronal cell line in suspension were carried out at X-band for closed chamber geometry. Oxygen consumption rates showed a linear dependence on the number of cells. Other significant benefits of the analyte are: the fast effective rotational diffusion and slow translational diffusion of the spin-probe is favorable for the measurements, and there is no cross reactivity between oxygen and paramagnetic ions in the lipid bilayer.
A doubly curved reflector X-band antenna with integrated IFF array
NASA Astrophysics Data System (ADS)
Alia, F.; Barbati, S.
Primary radar antennas and Identification Friend or Foe (IFF) antennas must rotate with the same speed and synchronism, so that the target echo and IFF transponder mark will appear to the operator at the same time and at the same angular direction. A doubly-curved reflector antenna with a six-element microstrip array integrated in the reflector surface is presented to meet this requirement. The main antenna operates at X-band for low angle search radar, while the secondary antenna operates at L-band for IFF functions. The new configuration minimizes masking of the X-band radiated energy as a result of the IFF L-band elements. In fact, the only effect of the microstrip array on the X-band radiation pattern is the presence of several sidelobes in the + or - 90 deg angular region. The proposed new solution is compared to three other L-band/X-band integrated antenna configurations, and is found to be more advantageous with respect to masking, mechanical aspects, and production costs.
NASA Astrophysics Data System (ADS)
Juliet sheela, K.; Krishnan, S. Radha; Shanmugam, V. M.; Subramanian, P.
2018-04-01
Electron paramagnetic resonance (EPR) studies have been investigated at X-band microwave frequency on Cu2+ ion incorporated into the single crystal of potassium succinate-succinic acid (KSSA) at room temperature. The angular variation of the EPR spectra has shown two magnetically in-equivalent Cu2+ sites in the KSSA single crystal system. The spin Hamiltonian parameters g and A are determined which reveals that the site I and site II occupied in rhombic and axial local field symmetry around the impurity ion. Among the two paramagnetic impurity ions, sites one occupies at substituitional position in the place of monovalent cation (K+) in the crystal whereas the other enters in its lattice interstitially by the correlation of EPR and crystal structure data. From the calculated principle values gxx, gyy, gzz and Axx, Ayy, Azz of both the sites, the admixture coefficients and molecular orbital coefficients were evaluated which gives the information of ground state wave function and types of bonding of impurity ions with the ligands.
Inflatable Antenna for CubeSat: Extension of the Previously Developed S-Band Design to the X-Band
NASA Technical Reports Server (NTRS)
Babuscia, Alessandra; Choi, Thomas; Cheung, Kar-Ming; Thangavelautham, Jekan; Ravichandran, Mithun; Chandra, Aman
2015-01-01
The inflatable antenna for CubeSat is a 1 meter antenna reflector designed with one side reflective Mylar, another side clear Mylar with a patch antenna at the focus. The development of this technology responds to the increasing need for more capable communication systems to allow CubeSats to operate autonomously in interplanetary missions. An initial version of the antenna for the S-Band was developed and tested in both anechoic chamber and vacuum chamber. Recent developments in transceivers and amplifiers for CubeSat at X-band motivated the extension from the S-Band to the X-Band. This paper describes the process of extending the design of the antenna to the X-Band focusing on patch antenna redesign, new manufacturing challenges and initial results of experimental tests.
Chemical trends of the luminescence in wide band gap II 1-xMn xVI semimagnetic semiconductors
NASA Astrophysics Data System (ADS)
Benecke, C.; Busse, W.; Gumlich, H.-E.
1990-04-01
Time resolved emission and excitation spectroscopy is used to investigate the Mn correlated luminescence in wide band gap II-VI compounds, i.e. Zn 1-xMn xS, Cd 1-xMn xSe, Zn 1-xMn xTe and Cd 1-xMn xTe. Additional Information has been obtained with CdxZnyMnzTe( x+ y+ z=1) in checking the luminescence by variation of the ratio of the cations Cd and Zn. Generally speaking, at least two distinct emissions bands can be observed for each II 1- xMn xVI compound. One emissions band is attributed to the internal transition 4T 1(G)→ 6A 1(S) of the 3d 5 electron of the Mn 2+ on regular metal sites with energies of about ≈2 eV. The other emission band is found to occur in the near infrared range of about ≈1.3 eV. This emission band is tentatively interpreted as a transition of Mn 2+ ions on interstitial sites or in small Mn chalcogenide clusters, both interpretations assuming cubic symmetry. This model is supported by the existence of low energy excitation bands and by the great similarity of the shape of the two emission bands which lead to comparable Huang-Rhys factors and effective phonon energies. Also the established trend in the experimental data of the II-VI compounds under consideration confirm this interpretation. For both the IR and the yellow Mn 2+ center, the Racah parameters B and C and the crystal field parameter Dq are determined on the basis of experimental data. As a result, the energy of both the emission and the excitation bands is predominantly determined by the sorrounding anions. These bands shift to higher energies when the anions are changed in the fixed order: Te→Se→S. Regularly, there is also a spectral shift when Zn is replaced by Cd, which is smaller than the shift due to the variation of onions.
Effect of magnetic coupling on non-radiative relaxation time of Fe3+ sites on LaAl1-xFexO3 pigments
NASA Astrophysics Data System (ADS)
Novatski, A.; Somer, A.; Maranha, F. G.; de Souza, E. C. F.; Andrade, A. V. C.; Antunes, S. R. M.; Borges, C. P. F.; Dias, D. T.; Medina, A. N.; Astrath, N. G. C.
2018-02-01
Inorganic pigments of the system LaAl1-xFexO3 were prepared by the Pechini and the Solid State Reaction (SSR) methods. Magnetic interactions and non-radiative relaxation time were analyzed by means of phase-resolved photoacoustic spectroscopy and electron paramagnetic resonance (EPR) techniques. EPR results show a change in the magnetic behavior from paramagnetic (x = 0.2 and 0.4) to antiferromagnetic (x = 1.0), which is believed to be a result of the SSR preparation method. Trends in the optical absorption bands of the Fe3+ are attributed to their electronic transitions, and the increase in the band's intensity at 480 and 550 nm was assigned to the increase in the magnetic coupling between Fe-Fe. The phase-resolved method is capable of distinguishing between the two preparation methods, and it is possible to infer that SSR modifies the magnetic coupling of Fe-Fe with x.
Jåstad, Eirik O; Torheim, Turid; Villeneuve, Kathleen M; Kvaal, Knut; Hole, Eli O; Sagstuen, Einar; Malinen, Eirik; Futsaether, Cecilia M
2017-09-28
The amino acid l-α-alanine is the most commonly used material for solid-state electron paramagnetic resonance (EPR) dosimetry, due to the formation of highly stable radicals upon irradiation, with yields proportional to the radiation dose. Two major alanine radical components designated R1 and R2 have previously been uniquely characterized from EPR and electron-nuclear double resonance (ENDOR) studies as well as from quantum chemical calculations. There is also convincing experimental evidence of a third minor radical component R3, and a tentative radical structure has been suggested, even though no well-defined spectral signature has been observed experimentally. In the present study, temperature dependent EPR spectra of X-ray irradiated polycrystalline alanine were analyzed using five multivariate methods in further attempts to understand the composite nature of the alanine dosimeter EPR spectrum. Principal component analysis (PCA), maximum likelihood common factor analysis (MLCFA), independent component analysis (ICA), self-modeling mixture analysis (SMA), and multivariate curve resolution (MCR) were used to extract pure radical spectra and their fractional contributions from the experimental EPR spectra. All methods yielded spectral estimates resembling the established R1 spectrum. Furthermore, SMA and MCR consistently predicted both the established R2 spectrum and the shape of the R3 spectrum. The predicted shape of the R3 spectrum corresponded well with the proposed tentative spectrum derived from spectrum simulations. Thus, results from two independent multivariate data analysis techniques strongly support the previous evidence that three radicals are indeed present in irradiated alanine samples.
Multisite EPR oximetry from multiple quadrature harmonics.
Ahmad, R; Som, S; Johnson, D H; Zweier, J L; Kuppusamy, P; Potter, L C
2012-01-01
Multisite continuous wave (CW) electron paramagnetic resonance (EPR) oximetry using multiple quadrature field modulation harmonics is presented. First, a recently developed digital receiver is used to extract multiple harmonics of field modulated projection data. Second, a forward model is presented that relates the projection data to unknown parameters, including linewidth at each site. Third, a maximum likelihood estimator of unknown parameters is reported using an iterative algorithm capable of jointly processing multiple quadrature harmonics. The data modeling and processing are applicable for parametric lineshapes under nonsaturating conditions. Joint processing of multiple harmonics leads to 2-3-fold acceleration of EPR data acquisition. For demonstration in two spatial dimensions, both simulations and phantom studies on an L-band system are reported. Copyright © 2011 Elsevier Inc. All rights reserved.
EPR spectroscopic investigations in 15BaO-25Li2O-(60-x) B2O3-xFe2O3 glass system
NASA Astrophysics Data System (ADS)
Bhogi, Ashok; Kumar, R. Vijaya; Kistaiah, P.
2018-05-01
Glasses with composition 15BaO-25Li2O-(60-x) B2O3 -xFe2O3 (x = 0, 0.2, 0.4, 0.6, 0.8 and 1 mol %) were prepared by the conventional melt quenching technique. These glasses were characterized using X-ray diffraction (XRD). Electron paramagnetic resonance (EPR) investigations have been carried out as a function of iron ion concentration. The observed EPR spectra of Fe3+ ion exhibits resonance signals at g= 2.0, 4.3 and 8.0. The resonance signal at g= 4.3 is due to isolated Fe3+ ions in site with rhombic symmetry where as the g= 2.0 resonance signal is attributed to the Fe3+ ions coupled by exchange interaction in a distorted octahedral environment and the signal at g= 8.0 arises from axially distorted sites. The number of spins participating in resonance (N) and its paramagnetic susceptibilities (χ) have also been evaluated. The peak-to-peak line width ΔB for the resonance lines at g ≈ 4.3 and at g ≈ 2.0 is increasing as function of the iron ion content. The line intensity of the resonance centered at g ≈ 4.3 and at g ≈ 2.0 increases up to 0.8 mol% of Fe2O3 and for 1 mol% of Fe2O3 its value is found to decrease. The analysis of these results indicated that the conversion some of Fe3+ cations to Fe2+ ions beyond 0.8 mol%.
Design and testing of a 750 MHz CW-EPR digital console for small animal imaging
NASA Astrophysics Data System (ADS)
Sato-Akaba, Hideo; Emoto, Miho C.; Hirata, Hiroshi; Fujii, Hirotada G.
2017-11-01
This paper describes the development of a digital console for three-dimensional (3D) continuous wave electron paramagnetic resonance (CW-EPR) imaging of a small animal to improve the signal-to-noise ratio and lower the cost of the EPR imaging system. A RF generation board, an RF acquisition board and a digital signal processing (DSP) & control board were built for the digital EPR detection. Direct sampling of the reflected RF signal from a resonator (approximately 750 MHz), which contains the EPR signal, was carried out using a band-pass subsampling method. A direct automatic control system to reduce the reflection from the resonator was proposed and implemented in the digital EPR detection scheme. All DSP tasks were carried out in field programmable gate array ICs. In vivo 3D imaging of nitroxyl radicals in a mouse's head was successfully performed.
Rye Canyon X-ray noise test: One-third octave-band data
NASA Technical Reports Server (NTRS)
Willshire, W. L., Jr.
1983-01-01
Acoustic data were obtained for the 25 ft. diameter X-wing rotor model during performance testing of the rotor system in hover. Data collected at the outdoor whirl tower test facility with a twelve microphone array were taken for approximately 150 test conditions comprised of various combinations of RPM, blade pressure ratio (BPR), and blade angle of attack (collective). The three test parameters had four values of RPM from 404 to 497, twelve values of BPR from 1.0 to 2.1, and six values of collective from 0.0 deg to 8.5 deg. Fifteen to twenty seconds of acoustic data were reduced to obtain an average 1/3 octave band spectrum for each microphone for each test condition. The complete, as measured, 1/3 octave band results for all the acoustic data are listed. Another part of the X-wing noise test was the acoustic calibration of the Rye Canyon whirl tower bowl. Corrections were computed which, when applied to as measured data, yield estimates of the free field X-wing noise. The free field estimates provide a more realistic measure of the rotor system noise levels. Trend analysis of the three test parameters on noise level were performed.
NASA Astrophysics Data System (ADS)
Kirillov, V. A.; Kuchuro, J. I.
2014-09-01
We have used EPR dosimetry on tooth enamel to show that the combined effect of x-rays with effective energy 34 keV and gamma radiation with average energy 1250 keV leads to a significant increase in the reconstructed absorbed dose compared with the applied dose from a gamma source or from an x-ray source or from both sources of electromagnetic radiation. In simulation experiments, we develop an approach to estimating the contribution of diagnostic x-rays to the exposure dose formed in the tooth enamel by the combined effect of x-rays and gamma radiation.
Wang, Zhenhai; Zhao, Mingwen; Wang, Xiaopeng; Xi, Yan; He, Xiujie; Liu, Xiangdong; Yan, Shishen
2012-12-05
The band alignment in ZnO-GaN and related heterostructures is crucial for uses in solar harvesting technology. Here, we report our density functional calculations of the band alignment and optical properties of ZnO-GaN and ZnO-(Ga(1-x)Zn(x))(N(1-x)O(x))-GaN heterostructures using a Heyd-Scuseria-Ernzerhof (HSE) hybrid functional. We found that the conventional GGA functionals underestimate not only the band gap but also the band offset of these heterostructures. Using the hybrid functional calculations, we show that the (Ga(1-x)Zn(x))(N(1-x)O(x)) solid solution has a direct band gap of about 2.608 eV, in good agreement with the experimental data. More importantly, this solid solution forms type-II band alignment with the host materials. A GaN-(Ga(1-x)Zn(x))(N(1-x)O(x))-ZnO core-shell solar cell model is presented to improve the visible light absorption ability and carrier collection efficiency.
NASA Astrophysics Data System (ADS)
An, Youngseo; Mahata, Chandreswar; Lee, Changmin; Choi, Sungho; Byun, Young-Chul; Kang, Yu-Seon; Lee, Taeyoon; Kim, Jiyoung; Cho, Mann-Ho; Kim, Hyoungsub
2015-10-01
Amorphous Ti1-x Al x O y films in the Ti-oxide-rich regime (x < 0.5) were deposited on p-type GaAs via atomic layer deposition with titanium isopropoxide, trimethylaluminum, and H2O precursor chemistry. The electrical properties and energy band alignments were examined for the resulting materials with their underlying substrates, and significant frequency dispersion was observed in the accumulation region of the Ti-oxide-rich Ti1-x Al x O y films. Although a further reduction in the frequency dispersion and leakage current (under gate electron injection) could be somewhat achieved through a greater addition of Al-oxide in the Ti1-x Al x O y film, the simultaneous decrease in the dielectric constant proved problematic in finding an optimal composition for application as a gate dielectric on GaAs. The spectroscopic band alignment measurements of the Ti-oxide-rich Ti1-x Al x O y films indicated that the band gaps had a rather slow increase with the addition of Al-oxide, which was primarily compensated for by an increase in the valance band offset, while a nearly-constant conduction band offset with a negative electron barrier height was maintained.
Increasing sensitivity of pulse EPR experiments using echo train detection schemes.
Mentink-Vigier, F; Collauto, A; Feintuch, A; Kaminker, I; Tarle, V; Goldfarb, D
2013-11-01
Modern pulse EPR experiments are routinely used to study the structural features of paramagnetic centers. They are usually performed at low temperatures, where relaxation times are long and polarization is high, to achieve a sufficient Signal/Noise Ratio (SNR). However, when working with samples whose amount and/or concentration are limited, sensitivity becomes an issue and therefore measurements may require a significant accumulation time, up to 12h or more. As the detection scheme of practically all pulse EPR sequences is based on the integration of a spin echo--either primary, stimulated or refocused--a considerable increase in SNR can be obtained by replacing the single echo detection scheme by a train of echoes. All these echoes, generated by Carr-Purcell type sequences, are integrated and summed together to improve the SNR. This scheme is commonly used in NMR and here we demonstrate its applicability to a number of frequently used pulse EPR experiments: Echo-Detected EPR, Davies and Mims ENDOR (Electron-Nuclear Double Resonance), DEER (Electron-Electron Double Resonance|) and EDNMR (Electron-Electron Double Resonance (ELDOR)-Detected NMR), which were combined with a Carr-Purcell-Meiboom-Gill (CPMG) type detection scheme at W-band. By collecting the transient signal and integrating a number of refocused echoes, this detection scheme yielded a 1.6-5 folds SNR improvement, depending on the paramagnetic center and the pulse sequence applied. This improvement is achieved while keeping the experimental time constant and it does not introduce signal distortion. Copyright © 2013 Elsevier Inc. All rights reserved.
Design and testing of a 750MHz CW-EPR digital console for small animal imaging.
Sato-Akaba, Hideo; Emoto, Miho C; Hirata, Hiroshi; Fujii, Hirotada G
2017-11-01
This paper describes the development of a digital console for three-dimensional (3D) continuous wave electron paramagnetic resonance (CW-EPR) imaging of a small animal to improve the signal-to-noise ratio and lower the cost of the EPR imaging system. A RF generation board, an RF acquisition board and a digital signal processing (DSP) & control board were built for the digital EPR detection. Direct sampling of the reflected RF signal from a resonator (approximately 750MHz), which contains the EPR signal, was carried out using a band-pass subsampling method. A direct automatic control system to reduce the reflection from the resonator was proposed and implemented in the digital EPR detection scheme. All DSP tasks were carried out in field programmable gate array ICs. In vivo 3D imaging of nitroxyl radicals in a mouse's head was successfully performed. Copyright © 2017 Elsevier Inc. All rights reserved.
Characterisation of [Cu4S], the catalytic site in nitrous oxide reductase, by EPR spectroscopy.
Oganesyan, Vasily S; Rasmussen, Tim; Fairhurst, Shirley; Thomson, Andrew J
2004-04-07
The enzyme nitrous oxide reductase (N(2)OR) has a unique tetranuclear copper centre [Cu(4)S], called Cu(Z), at the catalytic site for the two-electron reduction of N(2)O to N(2). The X- and Q-band EPR spectra have been recorded from two forms of the catalytic site of the enzyme N(2)OR from Paracoccus pantotrophus, namely, a form prepared anaerobically, Cu(Z), that undergoes a one-electron redox cycle and Cu(Z)*, prepared aerobically, which cannot be redox cycled. The spectra of both species are axial with that of Cu(Z) showing a rich hyperfine splitting in the g||-region at X-band. DFT calculations were performed to gain insight into the electronic configuration and ground-state properties of Cu(Z) and to calculate EPR parameters. The results for the oxidation state [Cu(+1)(3)Cu(+2)(1)S](3+) are in good agreement with values obtained from the fitting of experimental spectra, confirming the absolute oxidation state of Cu(Z). The unpaired spin density in this configuration is delocalised over four copper ions, thus, Cu(I) 20.1%, Cu(II) 9.5%, Cu(III) 4.8% and Cu(IV) 9.2%, the mu(4)-sulfide ion and oxygen ligand. The three copper ions carrying the highest spin density plus the sulfide ion lie approximately in the same plane while the fourth copper ion is perpendicular to this plane and carries only 4.8% spin density. It is suggested that the atoms in this plane represent the catalytic core of Cu(Z), allowing electron redistribution within the plane during interaction with the substrate, N(2)O.
Westphal, Anne; Klinkebiel, Arne; Berends, Hans-Martin; Broda, Henning; Kurz, Philipp; Tuczek, Felix
2013-03-04
The manganese(III) Schiff base complexes [Mn(acen)X] (H2acen: N,N'-ethylenebis(acetylacetone)imine, X: I(-), Br(-), Cl(-), NCS(-)) are considered as model systems for a combined study of the electronic structure using vibrational, UV/vis absorption, parallel-mode electron paramagnetic resonance (EPR) and low-temperature magnetic circular dichroism (MCD) spectroscopy. By variation of the co-ligand X, the influence of the axial ligand field within a given square-pyramidal coordination geometry on the UV/vis, EPR, and MCD spectra of the title compounds is investigated. Between 25000 and 35000 cm(-1), the low-temperature MCD spectra are dominated by two very intense, oppositely signed pseudo-A terms, referred to as "double pseudo-A terms", which change their signs within the [Mn(acen)X] series dependent on the axial ligand X. Based on molecular orbital (MO) and symmetry considerations, these features are assigned to π(n.b.)(s, a) → yz, z(2) ligand-to-metal charge transfer transitions. The individual MCD signs are directly determined from the calculated MOs of the [Mn(acen)X] complexes. The observed sign change is explained by an inversion of symmetry among the π(n.b.)(s, a) donor orbitals which leads to an interchange of the positive and negative pseudo-A terms constituting the "double pseudo-A term".
Small X-Band Oscillator Antennas
NASA Technical Reports Server (NTRS)
Lee, Richard Q.; Miranda, Felix A.; Clark, Eric B.; Wilt, David M.; Mueller, Carl H.; Kory, Carol L.; Lambert, Kevin M.
2009-01-01
A small, segmented microstrip patch antenna integrated with an X-band feedback oscillator on a high-permittivity substrate has been built and tested. This oscillator antenna is a prototype for demonstrating the feasibility of such devices as compact, low-power-consumption building blocks of advanced, lightweight, phased antenna arrays that would generate steerable beams for communication and remotesensing applications.
Extraction of Late Summer Sea Ice Properties from Polarimetric SAR Features in C- and X-Band
NASA Astrophysics Data System (ADS)
Fors, Ane S.; Brekke, Camilla; Gerland, Sebastian; Doulgeris, Anthony P.; Eltoft, Torbjørn
2015-04-01
In this study we examine the potential use of six polarimetric features for interpretation of late summer sea ice types. Five high-resolution C and X-band scenes were recorded in the Fram Strait covering fast first-year and old sea ice. In addition sea ice thickness, surface roughness and melt pond fraction were collected during a helicopter flight at the study area. From the SAR scenes, six polarimetric features were extracted. Along sections of the track of the helicopter flight, the mean of the SAR features were compared to mean values of the properties measured during the helicopter flight. The results reveal relations between several of the SAR features and the geophysical properties measured in C-band, and weak relations in X-band.
Preliminary Analysis of X-Band and Ka-Band Radar for Use in the Detection of Icing Conditions Aloft
NASA Technical Reports Server (NTRS)
Reehorst, Andrew L.; Koenig, George G.
2004-01-01
NASA and the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) have an on-going activity to develop remote sensing technologies for the detection and measurement of icing conditions aloft. Radar has been identified as a strong tool for this work. However, since the remote detection of icing conditions with the intent to identify areas of icing hazard is a new and evolving capability, there are no set requirements for radar sensitivity. This work is an initial attempt to quantify, through analysis, the sensitivity requirements for an icing remote sensing radar. The primary radar of interest for cloud measurements is Ka-band, however, since NASA is currently using an X-band unit, this frequency is also examined. Several aspects of radar signal analysis were examined. Cloud reflectivity was calculated for several forms of cloud using two different techniques. The Air Force Geophysical Laboratory (AFGL) cloud models, with different drop spectra represented by a modified gamma distribution, were utilized to examine several categories of cloud formation. Also a fundamental methods approach was used to allow manipulation of the cloud droplet size spectra. And an analytical icing radar simulator was developed to examine the complete radar system response to a configurable multi-layer cloud environment. Also discussed is the NASA vertical pointing X-band radar. The radar and its data system are described, and several summer weather events are reviewed.
EPR STUDIES OF THERMALLY STERILIZED VASELINUM ALBUM.
Ramos, Paweł; Pilawa, Barbara
2015-01-01
Electron paramagnetic resonance (EPR) spectroscopy was used for examination of free radicals in thermally treated vaselinum album (VA). Thermal treatment in hot air as sterilization process was tested. Conditions of thermal sterilization were chosen according to the pharmaceutical norms. Vaselinum album was heated at the following conditions (T--temperature, t--time): T = 160°C and t = 120 min, T = 170°C and t = 60 min and T = 180°C and t = 30 min. The aim of this work was to determine concentration and free radical properties of thermally sterilized VA. EPR analysis for VA was done 15 min after sterilization. EPR measurements were done at room temperature. EPR spectra were recorded in the range of microwave power of 2.2-70 mW. g-Factor, amplitudes (A) and line width (ΔBpp) of the spectra were determined. The shape of the EPR spectra was analyzed. Free radical concentration (N) in the heated samples was determined. EPR spectra were not obtained for the non heated VA. EPR spectra were detected for all thermally sterilized samples. The spectra revealed complex character, their asymmetry depends on microwave power. The lowest free radicals concentration was found for the VA sterilized at 180°C during 30 min. EPR spectroscopy is proposed as the method useful for optimization of sterilization process of drugs.
Band gap and mobility of epitaxial perovskite BaSn1 -xHfxO3 thin films
NASA Astrophysics Data System (ADS)
Shin, Juyeon; Lim, Jinyoung; Ha, Taewoo; Kim, Young Mo; Park, Chulkwon; Yu, Jaejun; Kim, Jae Hoon; Char, Kookrin
2018-02-01
A wide band-gap perovskite oxide BaSn O3 is attracting much attention due to its high electron mobility and oxygen stability. On the other hand, BaHf O3 was recently reported to be an effective high-k gate oxide. Here, we investigate the band gap and mobility of solid solutions of BaS n1 -xH fxO3 (x =0 -1 ) (BSHO) as a basis to build advanced perovskite oxide heterostructures. All the films were epitaxially grown on MgO substrates using pulsed laser deposition. Density functional theory calculations confirmed that Hf substitution does not create midgap states while increasing the band gap. From x-ray diffraction and optical transmittance measurements, the lattice constants and the band-gap values are significantly modified by Hf substitution. We also measured the transport properties of n -type La-doped BSHO films [(Ba ,La ) (Sn ,Hf ) O3 ] , investigating the feasibility of modulation doping in the BaSn O3/BSHO heterostructures. The Hall measurement data revealed that, as the Hf content increases, the activation rate of the La dopant decreases and the scattering rate of the electrons sharply increases. These properties of BSHO films may be useful for applications in various heterostructures based on the BaSn O3 system.
Clinical EPR: Unique Opportunities and Some Challenges
Swartz, Harold M.; Williams, Benjamin B.; Zaki, Bassem I.; Hartford, Alan C.; Jarvis, Lesley A.; Chen, Eunice; Comi, Richard J.; Ernstoff, Marc S.; Hou, Huagang; Khan, Nadeem; Swarts, Steven G.; Flood, Ann B.; Kuppusamy, Periannan
2014-01-01
Electron paramagnetic resonance (EPR) spectroscopy has been well established as a viable technique for measurement of free radicals and oxygen in biological systems, from in vitro cellular systems to in vivo small animal models of disease. However, the use of EPR in human subjects in the clinical setting, although attractive for a variety of important applications such as oxygen measurement, is challenged with several factors including the need for instrumentation customized for human subjects, probe and regulatory constraints. This paper describes the rationale and development of the first clinical EPR systems for two important clinical applications, namely, measurement of tissue oxygen (oximetry), and radiation dose (dosimetry) in humans. The clinical spectrometers operate at 1.2 GHz frequency and use surface loop resonators capable of providing topical measurements up to 1 cm depth in tissues. Tissue pO2 measurements can be carried out noninvasively and repeatedly after placement of an oxygen-sensitive paramagnetic material (currently India ink) at the site of interest. Our EPR dosimetry system is capable of measuring radiation-induced free radicals in the tooth of irradiated human subjects to determine the exposure dose. These developments offer potential opportunities for clinical dosimetry and oximetry, which include guiding therapy for individual patients with tumors or vascular disease, by monitoring of tissue oxygenation. Further work is in progress to translate this unique technology to routine clinical practice. PMID:24439333
Nitrogen-related intermediate band in P-rich GaN xP yAs 1-x-y alloys
DOE Office of Scientific and Technical Information (OSTI.GOV)
Zelazna, K.; Gladysiewicz, M.; Polak, M. P.
The electronic band structure of phosphorus-rich GaN xP yAs 1-x-y alloys (x ~ 0.025 and y ≥ 0.6) is studied experimentally using optical absorption, photomodulated transmission, contactless electroreflectance, and photoluminescence. Here, it is shown that incorporation of a few percent of N atoms has a drastic effect on the electronic structure of the alloys. The change of the electronic band structure is very well described by the band anticrossing (BAC) model in which localized nitrogen states interact with the extended states of the conduction band of GaAsP host. The BAC interaction results in the formation of a narrow intermediate bandmore » (E - band in BAC model) with the minimum at the Γ point of the Brillouin zone resulting in a change of the nature of the fundamental band gap from indirect to direct. The splitting of the conduction band by the BAC interaction is further confirmed by a direct observation of the optical transitions to the E + band using contactless electroreflectance spectroscopy.« less
Nitrogen-related intermediate band in P-rich GaN xP yAs 1-x-y alloys
Zelazna, K.; Gladysiewicz, M.; Polak, M. P.; ...
2017-11-16
The electronic band structure of phosphorus-rich GaN xP yAs 1-x-y alloys (x ~ 0.025 and y ≥ 0.6) is studied experimentally using optical absorption, photomodulated transmission, contactless electroreflectance, and photoluminescence. Here, it is shown that incorporation of a few percent of N atoms has a drastic effect on the electronic structure of the alloys. The change of the electronic band structure is very well described by the band anticrossing (BAC) model in which localized nitrogen states interact with the extended states of the conduction band of GaAsP host. The BAC interaction results in the formation of a narrow intermediate bandmore » (E - band in BAC model) with the minimum at the Γ point of the Brillouin zone resulting in a change of the nature of the fundamental band gap from indirect to direct. The splitting of the conduction band by the BAC interaction is further confirmed by a direct observation of the optical transitions to the E + band using contactless electroreflectance spectroscopy.« less
Nistor, Sergiu V; Stefan, Mariana; Goovaerts, Etienne; Ramaz, François; Briat, Bernard
2015-10-01
The sites of incorporation of Cu(2+) impurity ions in Bi12GeO20 single crystals co-doped with copper and vanadium have been investigated by electron paramagnetic resonance (EPR). While the X-band EPR spectra consist of a simple broad (ΔB ∼50 mT) line with anisotropic lineshape, the W-band EPR spectra exhibit well resolved, strongly anisotropic lines, due to transitions within the 3d(9)-(2)D ground manifold of the Cu(2+) ions. The most intense group of lines, attributed to the dominant Cu(2+)(I) center, displays a characteristic four components hyperfine structure for magnetic field orientations close to a 〈110〉 direction. The g and A tensor main axes are very close to one of the 12 possible sets of orthogonal 〈1-10〉, 〈00-1〉 and 〈110〉 crystal directions. Several less intense lines, with unresolved hyperfine structure and similar symmetry properties, mostly overlapped by the Cu(2+)(I) spectrum, were attributed to Cu(2+)(II) centers. The two paramagnetic centers are identified as substitutional Cu(2+) ions at Bi(3+) sites with low C1 symmetry, very likely resulting from different configurations of neighboring charge compensating defects. Copyright © 2015 Elsevier Inc. All rights reserved.
EPR spectroscopic investigation of psoriatic finger nails.
Nakagawa, Kouichi; Minakawa, Satoko; Sawamura, Daisuke
2013-11-01
Nail lesions are common features of psoriasis and found in almost half of the patients. However, there is no feasible spectroscopic method evaluating changes and severity of nail psoriasis. EPR (electron paramagnetic resonance) might be feasible for evaluating nail conditions in the patients of psoriasis. Finger nails of five cases with nail psoriasis, (three females and two males) were examined. Nail samples were subjected to the EPR assay. The small piece of the finger nail (1.5 × 5 mm(2)) was incubated in ~50 μM 5-DSA (5-doxylstearic acid) aqueous solutions for about 60 min at 37°C. After rinsing and wiping off the excess 5-DSA solution, the nail samples were measured by EPR. EPR spectra were analyzed using the intensity ratio (Fast/Slow) of the two motions at the peaks of the lower magnetic field. We observed two distinguishable sites on the basis of the EPR results. In addition, the modern EPR calculation was performed to analyze the spectra obtained. The nail psoriasis-related region is 2~3 times higher than that of the control. The present EPR results show that there are two distinguishable sites in the nail. In the case of nail psoriasis, the fragile components are 2~3 times more than those of the control. Thus, the EPR method is thought to be a novel and reliable method of evaluating the nail psoriasis. © 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.
NASA Astrophysics Data System (ADS)
Polak, M. P.; Scharoch, P.; Kudrawiec, R.
2017-05-01
A comprehensive and detailed study of the composition dependence of lattice constants, band gaps and band offsets has been performed for bulk Ge1-x Sn x alloy in the full composition range using state-of-the-art density functional theory methods. A spectral weight approach to band unfolding has been applied as a means of distinguishing the indirect and direct band gaps from folded supercell band structures. In this way, four characteristic regions of the band gap character have been identified for Ge1-x Sn x alloy: an indirect band gap (x < 6.5%), a direct band gap (6.5% < x < 25%) and an inverse band gap (x > 25%) with inverse spin-orbit split-off for 45% < x < 85%. In general, it has been observed that the bowing parameters of band edges (Γ and L-point in conduction band (CBΓ and CB L ), valence band (VB), and spin-orbit (SO) band) are rather large ({{b}\\text{C{{\\text{B}} Γ }}} = 2.43 ± 0.06 eV, {{b}\\text{C{{\\text{B}}L}}} = 0.64 ± 0.04 eV, {{b}\\text{VB}} = -0.59 ± 0.04 eV, and {{b}\\text{SO}} = -0.49 ± 0.05 eV). This indicates that Ge1-x Sn x behaves like a highly mismatched group IV alloy. The composition dependence of lattice constant shows negligible bowing (b a = -0.083 Å). Obtained results have been compared with available experimental data. The origin of band gap reduction and large bowing has been analyzed and conclusions have been drawn regarding the relationship between experimental and theoretical results. It is shown that due to the low DOS at the Γ-point, a significant filling of CB by electrons in the direct gap regime may easily take place. Therefore, the Burstein-Moss effect should be considered when comparing experimental data with theoretical predictions as has already been shown for other intrinsic n-type narrow gap semiconductors (e.g. InN).
NASA Astrophysics Data System (ADS)
Uchida, Takayuki; Jinno, Riena; Takemoto, Shu; Kaneko, Kentaro; Fujita, Shizuo
2018-04-01
The band alignment at an α-Ga2O3/α-(Al x Ga1‑ x )2O3 heterointerface, with different Al compositions (x), grown on a c-plane sapphire substrate was evaluated by X-ray photoelectron spectroscopy. The experimental results show that the heterointerface has the type-I band discontinuity with the valence band offsets of 0.090, 0.12, and 0.14 eV, and the conduction band offsets of 0.34, 0.79, and 1.87 eV, for x values of 0.1, 0.4, and 0.8, respectively. The small band offset for the valence band is attributed to the fact that the valence band of oxides is constituted by the localized O 2p level, which is dominated by the nature of oxygen atoms. The type-I band discontinuity is desirable for a variety of heterostructure devices.
X-band T/R switch with body-floating multi-gate PDSOI NMOS transistors
NASA Astrophysics Data System (ADS)
Park, Mingyo; Min, Byung-Wook
2018-03-01
This paper presents an X-band transmit/receive switch using multi-gate NMOS transistors in a silicon-on-insulator CMOS process. For low loss and high power handling capability, floating body multi-gate NMOS transistors are adopted instead of conventional stacked NMOS transistors, resulting in 53% reduction of transistor area. Comparing to the stacked NMOS transistors, the multi gate transistor shares the source and drain region between stacked transistors, resulting in reduced chip area and parasitics. The impedance between bodies of gates in multi-gate NMOS transistors is assumed to be very large during design and confirmed after measurement. The measured input 1 dB compression point is 34 dBm. The measured insertion losses of TX and RX modes are respectively 1.7 dB and 2.0 dB at 11 GHz, and the measured isolations of TX and RX modes are >27 dB and >20 dB in X-band, respectively. The chip size is 0.086 mm2 without pads, which is 25% smaller than the T/R switch with stacked transistors.
Very High Frequency Epr: Instrument and Applications
NASA Astrophysics Data System (ADS)
Wang, Wei
Most Electron Paramagnetic Resonance (EPR, also known as ESR or EMR) experiments are performed at conventional 9 GHz or 35 GHz frequency. But there are numerous situations in which a large increase in the microwave frequency (and/or magnetic field) will result in substantial increase in the information content in EPR spectra. This has motivated us to construct a very high frequency (VHF, 95 GHz) EPR spectrometer at Illinois EPR Research Center. Many advantages of VHF EPR are demonstrated through examples in Chapter 1. The spectrometer and some unique aspects of the instrument are described and documented in Chapter 2. Chapter 3 reports use of the VHF EPR technique to study the structure/spectral relationship of a homologous series of thiophenes, which may be constituents of coal. Two successful methods to generate the cation radicals of these organic sulfur compounds are found. The g matrices (tensors) of the thiophenic radicals are obtained for the first time. The small differences between anisotropic components of the g matrices can be unambiguously resolved. Correlations of the experimentally measured g matrices with the molecular and electronic structures are reported. The g shifts correlate linearly with lambda of their Huckel molecular orbitals; the largest g components are proportional to the pi spin densities on sulfur. In addition, the small proton hyperfine interactions of dibenzothiophene (DBT) are observed for the first time by continuous wave VHF EPR. A multifrequency approach, including auxiliary 2-4 GHz pulsed measurement, has shown that a single set of spin Hamiltonian parameters describes the spin system of DBT over a microwave frequency span of 3 to 95 GHz. These newly available, detailed, and accurate data provide a valuable opportunity to test, and perhaps to improve, the existing theoretical models for predictions on g matrices of organic radicals. Finally, Chapter 4 reports trial calculations of g matrices by several molecular orbital methods.
TerraSAR-X Measurements of Wind Fields, Ocean Waves and Currents
NASA Astrophysics Data System (ADS)
Lehner, S.; Schulz-Stellenfleth, J.; Brusch, S.
2008-01-01
TerraSAR-X is a new german X-band radar satellite launched on June 15, 2007. In this mission an operational spaceborne synthetic aperture radar (SAR) system with very high spatial resolution is set up producing remote sensing products for commercial and scientific use. TerraSAR-X is a scientific and technological continuation of the successful Space Shuttle missions SIR-C/X and SRTM.The spacecraft is equipped with a phased array X-band SAR, which can operate in different polarisations and has furthermore beam stearing capabilities. In addition the system has a split antenna mode, which is able to provide along track interferometric information. The instrument is designed for multiple imaging modes like Stripmap, Spotlight and ScanSAR.Due to its polarimetric and interferometric capabilities as well as the high spatial resolution of up to 1 m, the TerraSAR-X sensor is a very interesting tool for oceanography. The presentation will give an overview of several applications, which are of both scientific and commercial interest, like e.g. current and ocean wave measurements, monitoring of morphodynamical processes or high resolution wind field retrieval. The potential as well as limitations of the instrument will be summarized and compared with existing sensors. Necessary steps to translate existing C-band SAR inversion algorithms for wind and wave measurements to X-band will be discussed. A strategy will be outlined to achieve this by a combination of theoretical investigations and the use of existing experimental data acquired by both airborne and groundbased X-band radar. First results on the adaption of existing C-band wind retrieval algorithms will be presented. Wind and ocean wave parameter retrievals will be presented, e.g., based on TerraSAR-X scenes taken over the English channel.
X-ray absorption and reflection as probes of the GaN conduction bands: Theory and experiments
DOE Office of Scientific and Technical Information (OSTI.GOV)
Lambrecht, W.R.L.; Rashkeev, S.N.; Segall, B.
1997-04-01
X-ray absorption measurements are a well-known probe of the unoccupied states in a material. The same information can be obtained by using glancing angle X-ray reflectivity. In spite of several existing band structure calculations of the group III nitrides and previous optical studies in UV range, a direct probe of their conduction band densities of states is of interest. The authors performed a joint experimental and theoretical investigation using both of these experimental techniques for wurtzite GaN.
Time dependence of the radiation-induced EPR signal in sucrose.
Desrosiers, Marc; Wadley, Samara
2006-01-01
Sucrose and common household sugars (e.g. cane) have been studied as dosemeters for a wide variety of applications. However, previous studies of the post-irradiation time dependence of irradiated sugar did not include an electron paramagnetic resonance (EPR) reference material. This work employs synthetic ruby as an EPR reference material to remove significant spectrometer/environmental influences on the measured time-dependent changes in the EPR spectral amplitude of irradiated sucrose. As such, these more accurate measurements should replace the previously published data.
Hybrid functional study of band structures of GaAs1-xNx and GaSb1-xNx alloys
NASA Astrophysics Data System (ADS)
Virkkala, Ville; Havu, Ville; Tuomisto, Filip; Puska, Martti J.
2012-02-01
Band structures of GaAs1-xNx and GaSb1-xNx alloys are studied in the framework of the density functional theory within the hybrid functional scheme (HSE06). We find that the scheme gives a clear improvement over the traditional (semi)local functionals in describing, in a qualitative agreement with experiments, the bowing of electron energy band gap in GaAs1-xNx alloys. In the case of GaSb1-xNx alloys, the hybrid functional used makes the study of band structures possible ab initio without any empirical parameter fitting. We explain the trends in the band gap reductions in the two materials that result mainly from the positions of the nitrogen-induced states with respect to the bottoms of the bulk conduction bands.
Zhou, Yiying; Nelson, William H
2011-10-27
With K-band EPR (Electron Paramagnetic Resonance), ENDOR (Electron-Nuclear DOuble Resonance), and EIE (ENDOR-induced EPR) techniques, three free radicals (RI-RIII) in L-lysine hydrochloride dihydrate single crystals X-irradiated at 298 K were detected at 298 K, and six radicals (R1, R1', R2-R5) were detected if the temperature was lowered to 66 K from 298 K. R1 and RI dominated the central portion of the EPR at 66 and 298 K, respectively, and were identified as main chain deamination radicals, (-)OOCĊH(CH(2))(4)(NH(3))(+). R1' was identified as a main chain deamination radical with the different configuration from R1 at 66 K, and it probably formed during cooling the temperature from 298 to 66 K. The configurations of R1, R1', and RI were analyzed with their coupling tensors. R2 and R3 each contain one α- and four β-proton couplings and have very similar EIEs at three crystallographic axes. The two-layer ONIOM calculations (at B3LYP/6-31G(d,p):PM3) support that R2 and R3 are from different radicals: dehydrogenation at C4, (-)OOCCH(NH(3))(+)CH(2)ĊH(CH(2))(2)(NH(3))(+), and dehydrogenation at C5, (-)OOCCH(NH(3))(+)(CH(2))(2)ĊHCH(2)(NH(3))(+), respectively. The comparisons of the coupling tensors indicated that R2 (66 K) is the same radical as RII (298 K), and R3 is the same as RIII. Thus, RII and RIII also are the radicals of C4 and C5 dehydrogenation. R4 and R5 are minority radicals and were observed only when temperature was lowered to 66 K. R4 and R5 were only tentatively assigned as the side chain deamination radical, (-)OOCCH (NH(3))(+)(CH(2))(3)ĊH(2), and the radical dehydrogenation at C3, (-)OOCCH(NH(3))(+)ĊH(CH(2))(3)(NH(3))(+), respectively, although the evidence was indirect. From simulation of the EPR (B//a, 66 K), the concentrations of R1, R1', and R2-R5 were estimated as: R1, 50%; R1', 11%; R2, 14%; R3, 16%; R4, 6%; R5, 3%.
Design and experiment of a directional coupler for X-band long pulse high power microwaves.
Bai, Zhen; Li, Guolin; Zhang, Jun; Jin, Zhenxing
2013-03-01
Higher power and longer pulse are the trend of the development of high power microwave (HPM), and then some problems emerge in measuring the power of HPM because rf breakdown is easier to occur under the circumstance of high power (the level of gigawatt) and long pulse (about 100 ns). In order to measure the power of the dominant TM₀₁ mode of an X-band long pulse overmoded HPM source, a directional coupler with stable coupling coefficient, high directivity, and high power handling capacity in wide band is investigated numerically and experimentally. At the central frequency 9.4 GHz, the simulation results show that the coupling coefficient is -59.6 dB with the directivity of 35 dB and the power handling capacity of 2 GW. The coupling coefficient is calibrated to be accordant with the simulation results. The high power tests are performed on an X-band long pulse HPM source, whose output mode is mainly TM₀₁ mode, and the results show that the measured power and waveform of the directional coupler have a good consistency with the far-field measuring results.
A measurement of the vibrational band strength for the v3 band of the HO2 radical
NASA Technical Reports Server (NTRS)
Zahniser, M. S.; Stanton, A. C.
1984-01-01
Laboratory measurements of the v(3) band strength of HO2 using a tunable diode laser to measure the absorption strength of a vibration-rotation line in the P branch near 1080/cm are reported. The HO2 is generated in a discharge-flow system by reaction of fluorine atoms with excess H2O2: F + H2O2 - HO2 + HF. The HO2 concentration is determined from measurements of F-atom concentrations using both chemical titration with Cl2 and tunable diode laser absorption by the F-atom spin-orbit transition near 404/cm. The experimental data are consistent with a value of k(3) = (1.6 + or - 0.3) x 10 to the 12th cu cm/s and a ratio k(4)/k(1) = 1.0 + or - 0.4. The line strength for the 6(15) - 7(16)F(1) transition is 2.9 x 10 to the -21 sq cm/molecule/cm, which corresponds to a v(3) band strength of 35 + or - 9/sq cm/(STP atm). This value is a factor of 1.6 to 6 lower than previous ab initio calculations.
First-principle study of effect of variation of `x' on the band alignment in CZTS1-xSex
NASA Astrophysics Data System (ADS)
Ghemud, Vipul; Kshirsagar, Anjali
2018-04-01
The present work concentrates on the electronic structure study of CZTS1-xSex alloy with x ranging from 0 to 1. For the alloy study, we have carried out first-principles calculations employing generalized gradient approximation for structural optimization and further hybrid functional approach to compare the optical band gap with that obtained from the experiments. A systematic increase in the lattice parameters with lowering of band gap from 1.52eV to 1.04eV is seen with increasing Se concentration from 0 to 100%, however the lowering of valence band edge and conduction band edge is not linear with the concentration variation. Our results indicate that the lowering of band gap is a result increased Cu:d and Se:p hybridization with increasing `x'.
NASA Astrophysics Data System (ADS)
de Oliveira, Marcos; Wiegand, Thomas; Elmer, Lisa-Maria; Sajid, Muhammad; Kehr, Gerald; Erker, Gerhard; Magon, Claudio José; Eckert, Hellmut
2015-03-01
Anisotropic interactions present in three new nitroxide radicals prepared by N,N addition of NO to various borane-phosphane frustrated Lewis pairs (FLPs) have been characterized by continuous-wave (cw) and pulsed X-band EPR spectroscopies in solid FLP-hydroxylamine matrices at 100 K. Anisotropic g-tensor values and 11B, 14N, and 31P hyperfine coupling tensor components have been extracted from continuous-wave lineshape analyses, electron spin echo envelope modulation (ESEEM), and hyperfine sublevel correlation spectroscopy (HYSCORE) experiments with the help of computer simulation techniques. Suitable fitting constraints are developed on the basis of density functional theory (DFT) calculations. These calculations reveal that different from the situation in standard nitroxide radicals (TEMPO), the g-tensors are non-coincident with any of the nuclear hyperfine interaction tensors. The determination of these interaction parameters turns out to be successful, as the cw- and pulse EPR experiments are highly complementary in informational content. While the continuous-wave lineshape is largely influenced by the anisotropic hyperfine coupling to 14N and 31P, the ESEEM and HYSCORE spectra contain important information about the 11B hyperfine coupling and nuclear electric quadrupolar interaction. The set of cw- and pulsed EPR experiments, with fitting constraints developed by DFT calculations, defines an efficient strategy for the structural analysis of paramagnetic FLP adducts.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Oliveira, Marcos de; Magon, Claudio José; Wiegand, Thomas
2015-03-28
Anisotropic interactions present in three new nitroxide radicals prepared by N,N addition of NO to various borane-phosphane frustrated Lewis pairs (FLPs) have been characterized by continuous-wave (cw) and pulsed X-band EPR spectroscopies in solid FLP-hydroxylamine matrices at 100 K. Anisotropic g-tensor values and {sup 11}B, {sup 14}N, and {sup 31}P hyperfine coupling tensor components have been extracted from continuous-wave lineshape analyses, electron spin echo envelope modulation (ESEEM), and hyperfine sublevel correlation spectroscopy (HYSCORE) experiments with the help of computer simulation techniques. Suitable fitting constraints are developed on the basis of density functional theory (DFT) calculations. These calculations reveal that differentmore » from the situation in standard nitroxide radicals (TEMPO), the g-tensors are non-coincident with any of the nuclear hyperfine interaction tensors. The determination of these interaction parameters turns out to be successful, as the cw- and pulse EPR experiments are highly complementary in informational content. While the continuous-wave lineshape is largely influenced by the anisotropic hyperfine coupling to {sup 14}N and {sup 31}P, the ESEEM and HYSCORE spectra contain important information about the {sup 11}B hyperfine coupling and nuclear electric quadrupolar interaction. The set of cw- and pulsed EPR experiments, with fitting constraints developed by DFT calculations, defines an efficient strategy for the structural analysis of paramagnetic FLP adducts.« less
NASA Technical Reports Server (NTRS)
Iguchi, Toshio; Meneghini, Robert
1993-01-01
Air-borne radar measurements of thunderstorms were made as part of the CaPE (Convection and Precipitation/Electrification) experiment in Florida in July 1991. The radar has two channels, X-band (10 GHz) and Ka-band (34.5 GHz), and is capable of measuring cross-polarized returns as well as co-polarized returns. In stratiform rain, the cross-polarized components can be observed only at the bright band region and from the surface reflection. The linear depolarization ratios (LDR's) measured at X-band and Ka-band at the bright band are nearly equal. In convective rain, however, the LDR in Ka-band often exceeds the X-band LDR by several dB, and sometimes by more than 10 dB, reaching LDR values of up to -5 dB over heavy convective rain. For randomly oriented hydrometeors, such high LDR values cannot be explained by single scattering from non-spherical scattering particles alone. Because the LDR by single backscatter depends weakly on the wavelength, the difference between the Ka-band and X-band LDR's suggests that multiple scattering effects prevail in the Ka-band LDR. In order to test this inference, the magnitude of the cross-polarized component created by double scattering was calculated using the parameters of the airborne radar, which for both frequencies has beamwidths of 5.1 degrees and pulse widths of 0.5 microsecond. Uniform rain beyond the range of 3 km is assumed.
V x In (2–x) S 3 Intermediate Band Absorbers Deposited by Atomic Layer Deposition
McCarthy, Robert F.; Weimer, Matthew S.; Haasch, Richard T.; ...
2016-03-21
Substitutional alloys of several thin film semiconductors have been proposed as intermediate band (IB) materials for use in next-generation photovoltaics, which aim to utilize a larger fraction of the solar spectrum without sacrificing significant photovoltage. Here, we demonstrate a novel approach to IB material growth, namely atomic layer deposition (ALD), to enable unique control over substitutional-dopant location and density. Two new ALD processes for vanadium sulfide incorporation are introduced, one of which incorporates a vanadium (III) amidinate previously untested for ALD. We synthesize the first thin film V xIn (2-x)S 3 intermediate band semiconductors, using this process, and further demonstratemore » that the V:In ratio, and therefore intraband gap density of states, can be finely tuned according to the ALD dosing schedule. Deposition on a crystalline In 2S 3 underlayer promotes the growth of a tetragonal β-In 2S 3-like phase V xIn (2-x)S 3, which exhibits a distinct sub-band gap absorption peak with onset near 1.1 eV in agreement with computational predictions. But, the V xIn (2-x)S 3 films lack the lower energy transition predicted for a partially filled IB, and photoelectrochemical devices reveal a photocurrent response only from illumination with energy sufficient to span the parent band-gap.« less
Zdybel, Magdalena; Chodurek, Ewa; Pilawa, Barbara
2014-01-01
Free radicals in A-2058 human melanoma cells were studied by the use of electron paramagnetic resonance (EPR) spectroscopy. The aim of this work was to determine the changes in relative free radical concentrations in tumor A-2058 cells after treatment by valproic acid (VPA) and 5,7-dimethoxycoumarin (DMC). The influences of VPA and DMC on free radicals in A-2058 cells were compared with those for human melanoma malignum A-375 and G-361 cells, which were tested by us earlier. Human malignant melanoma A-2058 cells were exposed to interactions with VPA, DMC, and both VPA and DMC. The tumor cells A-2058 were purchased from LGC Standards (Lomianki, Poland), and they were grown in the standard conditions: at 37°C and in an atmosphere containing 95% air and 5% CO2, in the Minimum Essential Medium Eagle (MEM, Sigma-Aldrich). The A-2058 cells were incubated with VPA (1 mM) and DMC (10 μM) for 4 days. The first-derivative EPR spectra of the control A-2058 cells, and the cells treated with VPA, DMC, and both VPA and DMC, were measured by the electron paramagnetic resonance spectrometer of Radiopan (Poznań, Poland) with microwaves from an X-band (9.3 GHz). The parameters of the EPR lines: amplitudes (A), integral intensities (I), line widths (ΔBpp), and g-factors, were analyzed. The changes of amplitudes and line widths with microwave power increasing from 2.2 to 70 mW were drawn evaluated, o-Semiquinone free radicals of melanin biopolymer are mainly responsible for the EPR lines of A-2058 melanoma malignum cells. The amounts of free radicals in A-2058 cells treated with VPA, and both VPA and DMC, were lower than in the untreated control cells. Application of the tested substances (VPA, and both VPA and DMC) as the antitumor compounds was discussed. DMC without VPA did not decrease free radicals concentration in A-2058 cells. The studies con-firmed that EPR spectroscopy may be used to examine interactions of free radicals with antitumor compounds.
Sang, Ling; Zhu, Qin Sheng; Yang, Shao Yan; Liu, Gui Peng; Li, Hui Jie; Wei, Hong Yuan; Jiao, Chun Mei; Liu, Shu Man; Wang, Zhan Guo; Zhou, Xiao Wei; Mao, Wei; Hao, Yue; Shen, Bo
2014-01-01
The band offsets of non-polar A-plane GaN/AlN and AlN/GaN heterojunctions are measured by X-ray photoemission spectroscopy. A large forward-backward asymmetry is observed in the non-polar GaN/AlN and AlN/GaN heterojunctions. The valence-band offsets in the non-polar A-plane GaN/AlN and AlN/GaN heterojunctions are determined to be 1.33 ± 0.16 and 0.73 ± 0.16 eV, respectively. The large valence-band offset difference of 0.6 eV between the non-polar GaN/AlN and AlN/GaN heterojunctions is considered to be due to piezoelectric strain effect in the non-polar heterojunction overlayers.
Tropical-forest biomass estimation at X-Band from the spaceborne TanDEM-X interferometer
R. Treuhaft; F. Goncalves; J.R. dos Santos; M. Keller; M. Palace; S.N. Madsen; F. Sullivan; P.M.L.A. Graca
2014-01-01
This letter reports the sensitivity of X-band interferometric synthetic aperture radar (InSAR) data from the first dual-spacecraft radar interferometer, TanDEM-X, to variations in tropical-forest aboveground biomass (AGB). It also reports the first tropical-forest AGB estimates fromTanDEM-X data. Tropical forests account for...
CW- and pulsed-EPR of carbonaceous matter in primitive meteorites: solving a lineshape paradox.
Delpoux, Olivier; Gourier, Didier; Binet, Laurent; Vezin, Hervé; Derenne, Sylvie; Robert, François
2008-05-01
Insoluble organic matter (IOM) of Orgueil and Tagish Lake meteorites are studied by CW-EPR and pulsed-EPR spectroscopies. The EPR line is due to polycyclic paramagnetic moieties concentrated in defect-rich regions of the IOM, with concentrations of the order of 4x10(19) spin/g. CW-EPR reveals two types of paramagnetic defects: centres with S=1/2, and centres with S=0 ground state and thermally accessible triple state S=1. In spite of the Lorentzian shape of the EPR and its narrowing upon increasing the spin concentration, the EPR line is not in the exchange narrowing regime as previously deduced from multi-frequency CW-EPR [L. Binet, D. Gourier, Appl. Magn. Reson. 30 (2006) 207-231]. It is inhomogeneously broadened as demonstrated by the presence of nuclear modulations in the spin-echo decay. The line narrowing, similar to an exchange narrowing effect, is the result of an increasing contribution of the narrow line of the triplet state centres in addition to the broader line of doublet states. Hyperfine sublevel correlation spectroscopy (HYSCORE) of hydrogen and (13)C nuclei indicates that IOM* centres are small polycyclic moieties that are moderately branched with aliphatic chains, as shown by the presence of aromatic hydrogen atoms. On the contrary the lack of such aromatic hydrogen in triplet states suggests that these radicals are most probably highly branched. Paramagnetic centres are considerably enriched in deuterium, with D/H approximately 1.5+/-0.5x10(-2) of the order of values existing in interstellar medium.
A new design of an S/X dual band circular slot antenna for radar applications.
Ghnimi, Said; Wali, Rawia; Gharsallh, Ali; Razban, Tchanguiz
2013-01-01
A novel design of dual-band slot antenna with a circular patch for radar applications is presented and studied. It is fed by a micro-strip line and built on a FR-4 substrate with a whole size of 18 x 30 mm2. A dual band printed antenna is created by introducing slots on the radiating element. By this, two bandwidth, covering C and X band, are achieved. In order to obtain a good fundamental antenna design, the initial studies were carried out theoretically, using CST Microwave Studio simulation software. In this case, the frequency range at return loss < 10 dB is 5.24 - 6.16 GHz for low frequency and is 7.9 -11.7 GHz for high frequency. In addition, the proposed antenna has good radiation characteristics and stable gains over the whole operating bands. A prototype of antenna is fabricated and tested. Experimental data show good agreement between simulated and measured results.
Surface modification of TiO{sub 2} nanoparticles with carotenoids. EPR study
DOE Office of Scientific and Technical Information (OSTI.GOV)
Konovalova, T.A.; Kispert, L.D.; Konovalov, V.V.
1999-06-03
Among the semiconductors, titanium dioxide is the most suitable for many environmental applications. EPR measurements demonstrate efficient charge separation on carotenoid-modified titanium dioxide nanoparticles (7 nm). Strong complexation of carotenoids containing terminal carboxy groups ({minus}CO{sub 2}H) with the TiO{sub 2} surface leads to electron transfer from the adsorbed carotenoid molecule to the surface trapping site. For these systems, EPR signals of the carotenoid radical cations Car{sup {sm_bullet}+} and the electrons trapped on the TiO{sub 2} are observed before irradiation (77 K). Their UV-visible spectra show an absorption band with a maximum near 650 nm that is characteristic of the trappedmore » electrons. Surface modification of the TiO{sub 2} by other carotenoids results in the formation of a complex with an optical absorption band near 545 nm. These systems form charge-separated pairs [Car{sup {sm_bullet}+}{hor_ellipsis}TiO{sub 2}(e{sup {minus}}{sub tr}){sub surf}. TiO{sub 2}(e{sup {minus}}{sub tr}){sub latt}] only upon 365--600 nm illumination at 77 K. Complexation of the TiO{sub 2} colloids with carotenoids enhances spatial charge separation, shifts the absorption threshold into the visible region, and thus greatly improves the reducing ability of the semiconductor. Photoreduction of acceptor molecules such as 2,5-dichloro-1,4-benzoquinone, nitrobenzene, and oxygen is demonstrated.« less
Dai, Jun; Zhou, Pengxia; Lu, Junfeng; Zheng, Hongge; Guo, Jiyuan; Wang, Fang; Gu, Ning; Xu, Chunxiang
2016-01-14
Bandgap tunable semiconductor materials have wide application in integrated-optoelectronic and communication devices. The CdS1-xSex ternary semiconductor materials covering green-red bands have been reported previously, but their basic band-gap and optical properties crucial to the performance of the CdS1-xSex-based optoelectronic devices have not been deeply understood. In this paper, we theoretically simulated and discussed the feasibility of bandgap-tunable CdS1-xSex nanomaterials for designing wavelength tunable microlasers. Then we fabricated the CdS1-xSex nanobelts with their band gap ranging from 2.4 to 1.74 eV by adjusting the composition ratio x in the vapor-phase-transport growth process. The temperature-dependent photoluminescence and exciton-related optical constants of the CdS1-xSex nanobelts were carefully demonstrated. Finally, the wavelength-tunable Fabry-Perot lasing in CdS1-xSex nanobelts was obtained, and the Fabry-Perot lasing mechanism was numerically simulated by the FDTD method. The systematic results on the mechanism of the tunable band gap, exciton properties and lasing of the CdS1-xSex nanostructure help us deeply understand the intrinsic optical properties of this material, and will build a strong foundation for future application of green-red wavelength-tunable CdS1-xSex microlasers.
Shishkina, E A; Lyubashevskii, N M; Tolstykh, E I; Ignatiev, E A; Betenekova, T A; Nikiforov, S V
2001-09-01
A mathematical model for calculation of the 90Sr absorbed doses in dental tissues is presented. The results of the Monte-Carlo calculations are compared to the data obtained by EPR measurements of dental tissues. Radiometric measurements of the 90Sr concentrations. TLD and EPR dosimetry investigations were performed in animal (dog) study. The importance of the irregular 90Sr distribution in the dentine for absorbed dose formation has been shown. The dominant dose formation factors (main source-tissues) were identified for the crown dentine and enamel. The model has shown agreement with experimental data which allows to determine further directions of the human tooth model development.
Schultz, Kathryn M; Klug, Candice S
2017-12-01
The use of pressure is an advantageous approach to the study of protein structure and dynamics because it can shift the equilibrium populations of protein conformations toward higher energy states that are not of sufficient population to be observable at atmospheric pressure. Recently, the Hubbell group at the University of California, Los Angeles, reintroduced the application of high pressure to the study of proteins by electron paramagnetic resonance (EPR) spectroscopy. This methodology is possible using X-band EPR spectroscopy due to advances in pressure intensifiers, sample cells, and resonators. In addition to the commercial availability of the pressure generation and sample cells by Pressure Biosciences Inc., a five-loop-four-gap resonator required for the initial high pressure EPR spectroscopy experiments by the Hubbell group, and those reported here, was designed by James S. Hyde and built and modified at the National Biomedical EPR Center. With these technological advances, we determined the effect of pressure on the essential periplasmic lipopolysaccharide (LPS) transport protein from Escherichia coli , LptA, and one of its binding partners, LptC. LptA unfolds from the N-terminus to the C-terminus, binding of LPS does not appreciably stabilize the protein under pressure, and monomeric LptA unfolds somewhat more readily than oligomeric LptA upon pressurization to 2 kbar. LptC exhibits a fold and relative lack of stability upon LPS binding similar to LptA, yet adopts an altered, likely monomeric, folded conformation under pressure with only its C-terminus unraveling. The pressure-induced changes likely correlate with functional changes associated with binding and transport of LPS.
Subramanian, Sankaran; Koscielniak, Janusz W.; Devasahayam, Nallathamby; Pursley, Randall H.; Pohida, Thomas J.; Krishna, Murali C.
2007-01-01
Rapid field scan on the order of T/s using high frequency sinusoidal or triangular sweep fields superimposed on the main Zeeman field, was used for direct detection of signals without low-frequency field modulation. Simultaneous application of space-encoding rotating field gradients have been employed to perform fast CW EPR imaging using direct detection that could, in principle, approach the speed of pulsed FT EPR imaging. The method takes advantage of the well-known rapid-scan strategy in CW NMR and EPR that allows arbitrarily fast field sweep and the simultaneous application of spinning gradients that allows fast spatial encoding. This leads to fast functional EPR imaging and, depending on the spin concentration, spectrometer sensitivity and detection band width, can provide improved temporal resolution that is important to interrogate dynamics of spin perfusion, pharmacokinetics, spectral spatial imaging, dynamic oxymetry, etc. PMID:17350865
EPR, optical and superposition model study of Mn2+ doped L+ glutamic acid
NASA Astrophysics Data System (ADS)
Kripal, Ram; Singh, Manju
2015-12-01
Electron paramagnetic resonance (EPR) study of Mn2+ doped L+ glutamic acid single crystal is done at room temperature. Four interstitial sites are observed and the spin Hamiltonian parameters are calculated with the help of large number of resonant lines for various angular positions of external magnetic field. The optical absorption study is also done at room temperature. The energy values for different orbital levels are calculated, and observed bands are assigned as transitions from 6A1g(s) ground state to various excited states. With the help of these assigned bands, Racah inter-electronic repulsion parameters B = 869 cm-1, C = 2080 cm-1 and cubic crystal field splitting parameter Dq = 730 cm-1 are calculated. Zero field splitting (ZFS) parameters D and E are calculated by the perturbation formulae and crystal field parameters obtained using superposition model. The calculated values of ZFS parameters are in good agreement with the experimental values obtained by EPR.
Flood Monitoring using X-band Dual-polarization Radar Network
NASA Astrophysics Data System (ADS)
Chandrasekar, V.; Wang, Y.; Maki, M.; Nakane, K.
2009-09-01
A dense weather radar network is an emerging concept advanced by the Center for Collaborative Adaptive Sensing of the Atmosphere (CASA). Using multiple radars observing over a common will create different data outcomes depending on the characteristics of the radar units employed and the network topology. To define this a general framework is developed to describe the radar network space, and formulations are obtained that can be used for weather radar network characterization. Current weather radar surveillance networks are based upon conventional sensing paradigm of widely-separated, standalone sensing systems using long range radars that operate at wavelengths in 5-10 cm range. Such configuration has limited capability to observe close to the surface of the earth because of the earth's curvature but also has poorer resolution at far ranges. The dense network radar system, observes and measures weather phenomenon such as rainfall and severe weather close to the ground at higher spatial and temporal resolution compared to the current paradigm. In addition the dense network paradigm also is easily adaptable to complex terrain. Flooding is one of the most common natural hazards in the world. Especially, excessive development decreases the response time of urban watersheds and complex terrain to rainfall and increases the chance of localized flooding events over a small spatial domain. Successful monitoring of urban floods requires high spatiotemporal resolution, accurate precipitation estimation because of the rapid flood response as well as the complex hydrologic and hydraulic characteristics in an urban environment. This paper reviews various aspects in radar rainfall mapping in urban coverage using dense X-band dual-polarization radar networks. By reducing the maximum range and operating at X-band, one can ensure good azimuthal resolution with a small-size antenna and keep the radar beam closer to the ground. The networked topology helps to achieve satisfactory
NASA Astrophysics Data System (ADS)
Liu, Yi-Chi; Chuang, Keh-Shih; Yu, Cheng-Ching; Chao, Jiunn-Hsing; Hsu, Fang-Yuh
2015-11-01
Modern dental X-ray examination that consists of traditional form, panorama, and cone-beamed 3D technologies is one of the most frequent diagnostic applications nowadays. This study used the Rando Phantom and thermoluminescence dosimeters (TLD) to measure the absorbed doses of radiosensitive organs recommended by International Commission on Radiological Protection (ICRP), and whole body effective doses which were delivered due to dental X-ray examination performed with different types of X-ray instrument. Besides, enamel samples which performed reading with Electronic Paramagnetic Resonance (EPR) procedure were also used to estimate the tooth doses. EPR is a dose reconstruction method of measuring free radicals induced by radiation exposure to the calcified tissue (mainly in the tooth enamel or bone) to evaluate the accepted high dose. The tooth doses estimated by TLD and EPR methods were compared. Relationships between the tooth doses and effective doses by dental X-ray examinations with different types of X-ray equipment were investigated in this work.
NASA Astrophysics Data System (ADS)
Su, Linlin; Wang, Ying; Guo, Qinglin; Li, Xiaowei; Wang, Shufang; Fu, Guangsheng; Mazur, Yuriy I.; E Ware, Morgan; Salamo, Gregory J.; Liang, Baolai; Huffaker, Diana L.
2017-08-01
Optical properties of GaAs/Al x Ga1-x As quantum rings (QRs) grown on GaAs (1 0 0) by droplet epitaxy have been investigated as a function of the Al-composition in the Al x Ga1-x As barrier. A transition from type-I to type-II band alignment is observed for the QRs via photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements. While x ⩽ 0.45, the QR PL spectra show a blue-shift and an increasing intensity with increasing Al-composition, revealing the enhancement of quantum confinement in the QRs with type-I band alignment. While x ⩾ 0.60, the characteristic large blue-shift with excitation intensity and the much longer lifetime indicate the realization of a type-II band alignment. Due to the height fluctuation of QR structures grown by droplet epitaxy mode, it is not the large blue-shift of emission energy, but the long lifetime that becomes the more important feature to identify the type-II band alignment.
The continuous and discrete molecular orbital x-ray bands from Xe(q+) (12≤q≤29) +Zn collisions.
Guo, Yipan; Yang, Zhihu; Hu, Bitao; Wang, Xiangli; Song, Zhangyong; Xu, Qiumei; Zhang, Boli; Chen, Jing; Yang, Bian; Yang, Jie
2016-07-29
In this paper, the x-ray emissions are measured by the interaction of 1500-3500 keV Xe(q+) (q = 12, 15, 17, 19, 21, 23, 26 and 29) ions with Zn target. When q < 29, we observe Ll, Lα, Lβ1, Lβ2 and Lγ characteristic x-rays from Xe(q+) ions and a broad M-shell molecular orbital (MO) x-ray band from the transient quasi-molecular levels. It is found that their yields quickly increase with different rates as the incident energy increases. Besides, the widths of the broad MO x-ray bands are about 0.9-1.32 keV over the energy range studied and are proportional to v(1/2) (v = projectile velocity). Most remarkably, when the projectile charge state is 29, the broad x-ray band separates into several narrow discrete spectra, which was never observed before in this field.
Cheesman, Myles R; Oganesyan, Vasily S; Watmough, Nicholas J; Butler, Clive S; Thomson, Andrew J
2004-04-07
Fully oxidized cytochrome bo3 from Escherichia coli has been studied in its oxidized and several ligand-bound forms using electron paramagnetic resonance (EPR) and magnetic circular dichroism (MCD) spectroscopies. In each form, the spin-coupled high-spin Fe(III) heme o3 and CuB(II) ion at the active site give rise to similar fast-relaxing broad features in the dual-mode X-band EPR spectra. Simulations of dual-mode spectra are presented which show that this EPR can arise only from a dinuclear site in which the metal ions are weakly coupled by an anisotropic exchange interaction of J 1 cm-1. A variable-temperature and magnetic field (VTVF) MCD study is also presented for the cytochrome bo3 fluoride and azide derivatives. New methods are used to extract the contribution to the MCD of the spin-coupled active site in the presence of strong transitions from low-spin Fe(III) heme b. Analysis of the MCD data, independent of the EPR study, also shows that the spin-coupling within the active site is weak with J approximately 1 cm-1. These conclusions overturn a long-held view that such EPR signals in bovine cytochrome c oxidase arise from an S' = 2 ground state resulting from strong exchange coupling (J > 10(2) cm-1) within the active site.
NASA Astrophysics Data System (ADS)
Christiansen, Marie Bitsch; Sørensen, Mikkel Agerbæk; Sanyova, Jana; Bendix, Jesper; Simonsen, Kim Pilkjær
2017-03-01
In an investigation of the artists' materials used by P. S. Krøyer the contents of the tube colours found in Krøyer's painting cabinet were examined. In most cases, the results of the pigment analyses were as expected based on our knowledge of artists' colours used in the late 1800s and early 1900s. However, in one of the tube colours labelled "Jaune de Cadmium Citron" (cadmium lemon yellow) an extremely rare cadmium chromate pigment was found. The pigment was analysed and characterised by Raman microscopy (MRS), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), powder X-ray diffraction (PXRD), single-crystal X-ray crystallography, and electron paramagnetic resonance (EPR) spectroscopy. Cadmium chromate was synthesised by precipitation from an aqueous solution of cadmium nitrate and potassium chromate, and the resulting yellow crystals proved identical to the pigment found in the tube colour "Jaune de Cadmium Citron". The structure determined by single-crystal X-ray diffraction identified the pigment as 2CdCrO4·KOH·H2O or more accurately as KCd2(CrO4)2(H3O2) illustrating the μ-H3O2- species. The yellow colour of the paint sample taken from the tube had a greenish hue, which became even more prominent upon storage and drying. EPR analysis of the sample showed the presence of paramagnetic degradation products containing Cr(III) and Cr(V).
Christiansen, Marie Bitsch; Sørensen, Mikkel Agerbæk; Sanyova, Jana; Bendix, Jesper; Simonsen, Kim Pilkjær
2017-03-15
In an investigation of the artists' materials used by P. S. Krøyer the contents of the tube colours found in Krøyer's painting cabinet were examined. In most cases, the results of the pigment analyses were as expected based on our knowledge of artists' colours used in the late 1800s and early 1900s. However, in one of the tube colours labelled "Jaune de Cadmium Citron" (cadmium lemon yellow) an extremely rare cadmium chromate pigment was found. The pigment was analysed and characterised by Raman microscopy (MRS), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), powder X-ray diffraction (PXRD), single-crystal X-ray crystallography, and electron paramagnetic resonance (EPR) spectroscopy. Cadmium chromate was synthesised by precipitation from an aqueous solution of cadmium nitrate and potassium chromate, and the resulting yellow crystals proved identical to the pigment found in the tube colour "Jaune de Cadmium Citron". The structure determined by single-crystal X-ray diffraction identified the pigment as 2CdCrO 4 ·KOH·H 2 O or more accurately as KCd 2 (CrO 4 ) 2 (H 3 O 2 ) illustrating the μ-H 3 O 2 - species. The yellow colour of the paint sample taken from the tube had a greenish hue, which became even more prominent upon storage and drying. EPR analysis of the sample showed the presence of paramagnetic degradation products containing Cr(III) and Cr(V). Copyright © 2016 Elsevier B.V. All rights reserved.
Nichols, Joseph W; Bae, You Han
2014-09-28
The enhanced permeability and retention (EPR) of nanoparticles in tumors has long stood as one of the fundamental principles of cancer drug delivery, holding the promise of safe, simple and effective therapy. By allowing particles preferential access to tumors by virtue of size and longevity in circulation, EPR provided a neat rationale for the trend toward nano-sized drug carriers. Following the discovery of the phenomenon by Maeda in the mid-1980s, this rationale appeared to be well justified by the flood of evidence from preclinical studies and by the clinical success of Doxil. Clinical outcomes from nano-sized drug delivery systems, however, have indicated that EPR is not as reliable as previously thought. Drug carriers generally fail to provide superior efficacy to free drug systems when tested in clinical trials. A closer look reveals that EPR-dependent drug delivery is complicated by high tumor interstitial fluid pressure (IFP), irregular vascular distribution, and poor blood flow inside tumors. Furthermore, the animal tumor models used to study EPR differ from clinical tumors in several key aspects that seem to make EPR more pronounced than in human patients. On the basis of this evidence, we believe that EPR should only be invoked on a case-by-case basis, when clinical evidence suggests the tumor type is susceptible. Copyright © 2014 Elsevier B.V. All rights reserved.
Thétiot-Laurent, Sophie; Gosset, Gaëlle; Clément, Jean-Louis; Cassien, Mathieu; Mercier, Anne; Siri, Didier; Gaudel-Siri, Anouk; Rockenbauer, Antal; Culcasi, Marcel; Pietri, Sylvia
2017-02-01
There is increasing interest in measuring pH in biological samples by using nitroxides with pH-dependent electron paramagnetic resonance (EPR) spectra. Aiming to improve the spectral sensitivity (Δa X ) of these probes (i.e., the difference between the EPR hyperfine splitting (hfs) in their protonated and unprotonated forms), we characterized a series of novel linear α-carboxy, α'-diethoxyphosphoryl nitroxides constructed on an amino acid core and featuring an (α or α')-C-H bond. In buffer, the three main hfs (a N , a H , and a P ) of their EPR spectra vary reversibly with pH and, from a P or a H titration curves, a two- to fourfold increase in sensitivity was achieved compared to reference imidazoline or imidazolidine nitroxides. The crystallized carboxylate 10 b (pK a ≈3.6), which demonstrated low cytotoxicity and good resistance to bioreduction, was applied to probe stomach acidity in rats. The results pave the way to a novel generation of highly sensitive EPR pH markers. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
Nuclear spin-lattice relaxation in nitroxide spin-label EPR.
Marsh, Derek
2016-11-01
Nuclear relaxation is a sensitive monitor of rotational dynamics in spin-label EPR. It also contributes competing saturation transfer pathways in T 1 -exchange spectroscopy, and the determination of paramagnetic relaxation enhancement in site-directed spin labelling. A survey shows that the definition of nitrogen nuclear relaxation rate W n commonly used in the CW-EPR literature for 14 N-nitroxyl spin labels is inconsistent with that currently adopted in time-resolved EPR measurements of saturation recovery. Redefinition of the normalised 14 N spin-lattice relaxation rate, b=W n /(2W e ), preserves the expressions used for CW-EPR, whilst rendering them consistent with expressions for saturation recovery rates in pulsed EPR. Furthermore, values routinely quoted for nuclear relaxation times that are deduced from EPR spectral diffusion rates in 14 N-nitroxyl spin labels do not accord with conventional analysis of spin-lattice relaxation in this three-level system. Expressions for CW-saturation EPR with the revised definitions are summarised. Data on nitrogen nuclear spin-lattice relaxation times are compiled according to the three-level scheme for 14 N-relaxation: T 1 n =1/W n . Results are compared and contrasted with those for the two-level 15 N-nitroxide system. Copyright © 2016 Elsevier Inc. All rights reserved.
Measurement accuracies in band-limited extrapolation
NASA Technical Reports Server (NTRS)
Kritikos, H. N.
1982-01-01
The problem of numerical instability associated with extrapolation algorithms is addressed. An attempt is made to estimate the bounds for the acceptable errors and to place a ceiling on the measurement accuracy and computational accuracy needed for the extrapolation. It is shown that in band limited (or visible angle limited) extrapolation the larger effective aperture L' that can be realized from a finite aperture L by over sampling is a function of the accuracy of measurements. It is shown that for sampling in the interval L/b absolute value of xL, b1 the signal must be known within an error e sub N given by e sub N squared approximately = 1/4(2kL') cubed (e/8b L/L')(2kL') where L is the physical aperture, L' is the extrapolated aperture, and k = 2pi lambda.
Modelling Ground Based X- and Ku-Band Observations of Tundra Snow
NASA Astrophysics Data System (ADS)
Kasurak, A.; King, J. M.; Kelly, R. E.
2012-12-01
As part of a radar-based remote sensing field experiment in Churchill, Manitoba ground based Ku- and X-band scatterometers were deployed to observe changing tundra snowpack conditions from November 2010 to March 2011. The research is part of the validation effort for the Cold Regions Hydrology High-resolution Observatory (CoReH2O) mission, a candidate in the European Space Agency's Earth Explorer program. This paper focuses on the local validation of the semi-empirical radiative transfer (sRT) model proposed for use in snow property retrievals as part of the CoReH2O mission. In this validation experiment, sRT was executed in the forward mode, simulating backscatter to assess the ability of the model. This is a necessary precursor to any inversion attempt. Two experiments are considered, both conducted in a hummocky tundra environment with shallow snow cover. In both cases, scatterometer observations were acquired over a field of view of approximately 10 by 20 meters. In the first experiment, radar observations were made of a snow field and then repeated after the snow had been removed. A ground-based scanning LiDAR system was used to characterize the spatial variability of snow depth through measurements of the snow and ground surface. Snow properties were determined in the field of view from two snow pits, 12 density core measurements, and Magnaprobe snow depth measurements. In the second experiment, a site was non-destructively observed from November through March, with snow properties measured out-of-scene, to characterize the snow evolution response. The model results from sRT fit the form of the observations from the two scatterometer field experiments but do not capture the backscatter magnitude. A constant offset for the season of 5 dB for X-band co- and cross-polarization response was required to match observations, in addition to a 3 dB X- and Ku-band co-polarization offset after the 6th of December. To explain these offsets, it is recognized that the two
Band alignment at the Cu2ZnSn(SxSe1-x)4/CdS interface
NASA Astrophysics Data System (ADS)
Haight, Richard; Barkhouse, Aaron; Gunawan, Oki; Shin, Byungha; Copel, Matt; Hopstaken, Marinus; Mitzi, David B.
2011-06-01
Energy band alignments between CdS and Cu2ZnSn(SxSe1-x)4 (CZTSSe) grown via solution-based and vacuum-based deposition routes were studied as a function of the [S]/[S+Se] ratio with femtosecond laser ultraviolet photoelectron spectroscopy, photoluminescence, medium energy ion scattering, and secondary ion mass spectrometry. Band bending in the underlying CZTSSe layer was measured via pump/probe photovoltage shifts of the photoelectron spectra and offsets were determined with photoemission under flat band conditions. Increasing the S content of the CZTSSe films produces a valence edge shift to higher binding energy and increases the CZTSSe band gap. In all cases, the CdS conduction band offsets were spikes.
Broad-Band Measurements of Cen X-3 With XTE and CGRO
NASA Technical Reports Server (NTRS)
Vestrand, W. Thomas
1999-01-01
Centaurus X-3 has played a key role in the development of our understanding of galactic x-ray binary sources. Timing analysis of the UHURU x-ray observations for the luminous Cen X-3 source (L approximately 10(exp 38) erg/s) revealed the first evidence for coherent x-ray pulsations from an object in a binary system (Giaconni 1971; Schreier 1972). It was quickly understood that the luminous pulsed x-ray emission could be generated by the accretion of matter from a companion star onto a rotating neutron star and led to the adoption of binary star models as the fundamental model for galactic x-ray sources (e.g. Pringle and Rees 1972; Lamb 1973). Based on modeling and refined observations since the original measurements, we now believe that Cen X-3 is a high mass x-ray binary system that contains a disk-fed pulsar with a period of 4.84 seconds that is in a 2.087 day orbit around an O-star companion. Since the pulsar discovery, its period has been intermittently monitored and those studies show a long term spin-up of the pulsar punctuated by short intervals of spin-down (e.g. Finger 1994). The implied torques are thought to originate from the interaction of an accretion disk with the magnetic field of a neutron star (Ghosh and Lamb 1979).
ENDOR with band-selective shaped inversion pulses
NASA Astrophysics Data System (ADS)
Tait, Claudia E.; Stoll, Stefan
2017-04-01
Electron Nuclear DOuble Resonance (ENDOR) is based on the measurement of nuclear transition frequencies through detection of changes in the polarization of electron transitions. In Davies ENDOR, the initial polarization is generated by a selective microwave inversion pulse. The rectangular inversion pulses typically used are characterized by a relatively low selectivity, with full inversion achieved only for a limited number of spin packets with small resonance offsets. With the introduction of pulse shaping to EPR, the rectangular inversion pulses can be replaced with shaped pulses with increased selectivity. Band-selective inversion pulses are characterized by almost rectangular inversion profiles, leading to full inversion for spin packets with resonance offsets within the pulse excitation bandwidth and leaving spin packets outside the excitation bandwidth largely unaffected. Here, we explore the consequences of using different band-selective amplitude-modulated pulses designed for NMR as the inversion pulse in ENDOR. We find an increased sensitivity for small hyperfine couplings compared to rectangular pulses of the same bandwidth. In echo-detected Davies-type ENDOR, finite Fourier series inversion pulses combine the advantages of increased absolute ENDOR sensitivity of short rectangular inversion pulses and increased sensitivity for small hyperfine couplings of long rectangular inversion pulses. The use of pulses with an almost rectangular frequency-domain profile also allows for increased control of the hyperfine contrast selectivity. At X-band, acquisition of echo transients as a function of radiofrequency and appropriate selection of integration windows during data processing allows efficient separation of contributions from weakly and strongly coupled nuclei in overlapping ENDOR spectra within a single experiment.
Permanent magnet focused X-band photoinjector
Yu, David U. L.; Rosenzweig, James
2002-09-10
A compact high energy photoelectron injector integrates the photocathode directly into a multicell linear accelerator with no drift space between the injection and the linac. High electron beam brightness is achieved by accelerating a tightly focused electron beam in an integrated, multi-cell, X-band rf linear accelerator (linac). The photoelectron linac employs a Plane-Wave-Transformer (PWT) design which provides strong cell-to-cell coupling, easing manufacturing tolerances and costs.
Skew Projection of Echo-Detected EPR Spectra for Increased Sensitivity and Resolution
Bowman, Michael K.; Krzyaniak, Matthew D.; Cruce, Alex A.; Weber, Ralph T.
2013-01-01
The measurement of EPR spectra during pulsed EPR experiments is commonly accomplished by recording the integral of the electron spin echo as the applied magnetic field is stepped through the spectrum. This approach to echo-detected EPR spectral measurement (ED-EPR) limits sensitivity and spectral resolution and can cause gross distortions in the resulting spectra because some of the information present in the electron spin echo is discarded in such measurements. However, Fourier Transformation of echo shapes measured at a series of magnetic field values followed by skew projection onto either a magnetic field or resonance frequency axis can increase both spectral resolution and sensitivity without the need to trade one against the other. Examples of skew-projected spectra with single crystals, glasses and powders show resolution improvements as large as a factor of seven with sensitivity increases of as much as a factor of five. PMID:23644351
Skew projection of echo-detected EPR spectra for increased sensitivity and resolution
NASA Astrophysics Data System (ADS)
Bowman, Michael K.; Krzyaniak, Matthew D.; Cruce, Alex A.; Weber, Ralph T.
2013-06-01
The measurement of EPR spectra during pulsed EPR experiments is commonly accomplished by recording the integral of the electron spin echo as the applied magnetic field is stepped through the spectrum. This approach to echo-detected EPR spectral measurement (ED-EPR) limits sensitivity and spectral resolution and can cause gross distortions in the resulting spectra because some of the information present in the electron spin echo is discarded in such measurements. However, Fourier transformation of echo shapes measured at a series of magnetic field values followed by skew projection onto either a magnetic field or resonance frequency axis can increase both spectral resolution and sensitivity without the need to trade one against the other. Examples of skew-projected spectra with single crystals, glasses and powders show resolution improvements as large as a factor of seven with sensitivity increases of as much as a factor of five.
Homogeneity and EPR metrics for assessment of regular grids used in CW EPR powder simulations.
Crăciun, Cora
2014-08-01
CW EPR powder spectra may be approximated numerically using a spherical grid and a Voronoi tessellation-based cubature. For a given spin system, the quality of simulated EPR spectra depends on the grid type, size, and orientation in the molecular frame. In previous work, the grids used in CW EPR powder simulations have been compared mainly from geometric perspective. However, some grids with similar homogeneity degree generate different quality simulated spectra. This paper evaluates the grids from EPR perspective, by defining two metrics depending on the spin system characteristics and the grid Voronoi tessellation. The first metric determines if the grid points are EPR-centred in their Voronoi cells, based on the resonance magnetic field variations inside these cells. The second metric verifies if the adjacent Voronoi cells of the tessellation are EPR-overlapping, by computing the common range of their resonance magnetic field intervals. Beside a series of well known regular grids, the paper investigates a modified ZCW grid and a Fibonacci spherical code, which are new in the context of EPR simulations. For the investigated grids, the EPR metrics bring more information than the homogeneity quantities and are better related to the grids' EPR behaviour, for different spin system symmetries. The metrics' efficiency and limits are finally verified for grids generated from the initial ones, by using the original or magnetic field-constraint variants of the Spherical Centroidal Voronoi Tessellation method. Copyright © 2014 Elsevier Inc. All rights reserved.
Antioxidant Capacity: Experimental Determination by EPR Spectroscopy and Mathematical Modeling.
Polak, Justyna; Bartoszek, Mariola; Chorążewski, Mirosław
2015-07-22
A new method of determining antioxidant capacity based on a mathematical model is presented in this paper. The model was fitted to 1000 data points of electron paramagnetic resonance (EPR) spectroscopy measurements of various food product samples such as tea, wine, juice, and herbs with Trolox equivalent antioxidant capacity (TEAC) values from 20 to 2000 μmol TE/100 mL. The proposed mathematical equation allows for a determination of TEAC of food products based on a single EPR spectroscopy measurement. The model was tested on the basis of 80 EPR spectroscopy measurements of herbs, tea, coffee, and juice samples. The proposed model works for both strong and weak antioxidants (TEAC values from 21 to 2347 μmol TE/100 mL). The determination coefficient between TEAC values obtained experimentally and TEAC values calculated with proposed mathematical equation was found to be R(2) = 0.98. Therefore, the proposed new method of TEAC determination based on a mathematical model is a good alternative to the standard EPR method due to its being fast, accurate, inexpensive, and simple to perform.
The Celestial Reference Frame at X/Ka-band (8.4/32 GHz)
NASA Technical Reports Server (NTRS)
Jacobs, C. S.; Clark, J. E.; Heflin, M. B.; Skjerve, L. J.; Sovers, O. J.; Garcia-Miro, C.; Moll, V. E.; Horiuchi, S.
2011-01-01
A celestial reference frame at X/Ka-band (8.4/32 GHz) has been constructed using fifty-one 24-hour sessions with the Deep Space Network. We report on observations which have detected 436 sources covering the full 24 hours of right ascension and declinations down to -45 deg. Comparison of this X/Ka-band frame to the S/X-band (2.3/8.4 GHz) ICRF2 shows wRMS agreement of 200 micro-arcsec in a cos delta and 290 micro-arcsec in delta. There is evidence for zonal errors at the 100 micro-arcsec level. Known errors include limited SNR, lack of phase calibration, troposphere mismodelling, and limited southern geometry. The motivations for extending the ICRF to frequencies above 8 GHz are to access more compact source morphology for improved frame stability, to provide calibrators for phase referencing, and to support spacecraft navigation at Ka-band.
Two-dimensional wide-band-gap nitride semiconductors: Single-layer 1 T -X N2 (X =S ,Se , and Te )
NASA Astrophysics Data System (ADS)
Lin, Jia-He; Zhang, Hong; Cheng, Xin-Lu; Miyamoto, Yoshiyuki
2016-11-01
Recently, the two-dimensional (2D) semiconductors arsenene and antimonene, with band gaps larger than 2.0 eV, have attracted tremendous interest, especially for potential applications in optoelectronic devices with a photoresponse in the blue and UV range. Motivated by this exciting discovery, types of highly stable wide-band-gap 2D nitride semiconductors were theoretically designed. We propose single-layer 1 T -X N2 (X =S , Se, and Te) via first-principles simulations. We compute 1 T -X N2 (X =S , Se, and Te) with indirect band gaps of 2.825, 2.351, and 2.336 eV, respectively. By applying biaxial strain, they are able to induce the transition from a wide-band-gap semiconductor to a metal, and the range of absorption spectra of 1 T -X N2 (X =S , Se, and Te) obviously extend from the ultraviolet region to the blue-purple light region. With an underlying graphene, we find that 1 T -X N2 can completely shield the light absorption of graphene in the range of 1-1.6 eV. Our research paves the way for optoelectronic devices working under blue or UV light, and mechanical sensors based on these 2D crystals.
Emergency EPR and OSL dosimetry with table vitamins and minerals.
Sholom, S; McKeever, S W S
2016-12-01
Several table vitamins, minerals and L-lysine amino acid have been preliminarily tested as potential emergency dosemeters using electron paramagnetic resonance (EPR) and optically stimulated luminescence (OSL) techniques. Radiation-induced EPR signals were detected in samples of vitamin B2 and L-lysine while samples of multivitamins of different brands as well as mineral Mg demonstrated prominent OSL signals after exposure to ionizing radiation doses. Basic dosimetric properties of the radiation-sensitive substances were studied, namely dose response, fading of the EPR or OSL signals and values of minimum measurable doses (MMDs). For EPR-sensitive samples, the EPR signal is converted into units of dose using a linear dose response and correcting for fading using the measured fading dependence. For OSL-sensitive materials, a multi-aliquot, enhanced-temperature protocol was developed to avoid the problem of sample sensitization and to minimize the influence of signal fading. The sample dose in this case is also evaluated using the dose response and fading curves. MMDs of the EPR-sensitive samples were below 2 Gy while those of the OSL-sensitive materials were below 500 mGy as long as the samples are analyzed within 1 week after exposure. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.
Kaufmann, Royi; Yadid, Itamar; Goldfarb, Daniella
2013-05-01
Rapid freeze quench electron paramagnetic resonance (RFQ)-EPR is a method for trapping short lived intermediates in chemical reactions and subjecting them to EPR spectroscopy investigation for their characterization. Two (or more) reacting components are mixed at room temperature and after some delay the mixture is sprayed into a cold trap and transferred into the EPR tube. A major caveat in using commercial RFQ-EPR for high field EPR applications is the relatively large amount of sample needed for each time point, a major part of which is wasted as the dead volume of the instrument. The small sample volume (∼2μl) needed for high field EPR spectrometers, such as W-band (∼3.5T, 95GHz), that use cavities calls for the development of a microfluidic based RFQ-EPR apparatus. This is particularly important for biological applications because of the difficulties often encountered in producing large amounts of intrinsically paramagnetic proteins and spin labeled nucleic acid and proteins. Here we describe a dedicated microfluidic based RFQ-EPR apparatus suitable for small volume samples in the range of a few μl. The device is based on a previously published microfluidic mixer and features a new ejection mechanism and a novel cold trap that allows collection of a series of different time points in one continuous experiment. The reduction of a nitroxide radical with dithionite, employing the signal of Mn(2+) as an internal standard was used to demonstrate the performance of the microfluidic RFQ apparatus. Copyright © 2013 Elsevier Inc. All rights reserved.
Design and application of multimegawatt X -band deflectors for femtosecond electron beam diagnostics
Dolgashev, Valery A.; Bowden, Gordon; Ding, Yuantao; ...
2014-10-02
Performance of the x-ray free electron laser Linac Coherent Light Source (LCLS) and the Facility for Advanced Accelerator Experimental Tests (FACET) is determined by the properties of their extremely short electron bunches. Multi-GeV electron bunches in both LCLS and FACET are less than 100 fs long. Optimization of beam properties and understanding of free-electron laser operation require electron beam diagnostics with time resolution of about 10 fs. We designed, built and commissioned a set of high frequency X-band deflectors which can measure the beam longitudinal space charge distribution and slice energy spread to better than 10 fs resolution at fullmore » LCLS energy (14 GeV), and with 70 fs resolution at full FACET energy (20 GeV). Use of high frequency and high gradient in these devices allows them to reach unprecedented performance. We report on the physics motivation, design considerations, operational configuration, cold tests, and typical results of the X-band deflector systems currently in use at SLAC.« less
Sanyal, Bhaskar; Ahn, Jae-Jun; Maeng, Jeong-Hwan; Kyung, Hyun-Kyu; Lim, Ha-Kyeong; Sharma, Arun; Kwon, Joong-Ho
2014-09-01
Changes in cumin and chili powder from India resulting from electron-beam irradiation were investigated using 3 analytical methods: electronic nose (E-nose), Fourier transform infrared (FTIR) spectroscopy, and electron paramagnetic resonance (EPR) spectroscopy. The spices had been exposed to 6 to 14 kGy doses recommended for microbial decontamination. E-nose measured a clear difference in flavor patterns of the irradiated spices in comparison with the nonirradiated samples. Principal component analysis further showed a dose-dependent variation. FTIR spectra of the samples showed strong absorption bands at 3425, 3007 to 2854, and 1746 cm(-1). However, both nonirradiated and irradiated spice samples had comparable patterns without any noteworthy changes in functional groups. EPR spectroscopy of the irradiated samples showed a radiation-specific triplet signal at g = 2.006 with a hyper-fine coupling constant of 3 mT confirming the results obtained with the E-nose technique. Thus, E-nose was found to be a potential tool to identify irradiated spices. © 2014 Institute of Food Technologists®
NASA Technical Reports Server (NTRS)
Woo, Jonathan W.; Clark, George W.; Day, Charles S. R.; Nagase, Fumiaki; Takeshima, Toshiaki
1994-01-01
We have measured the decaying dust-scattered X-ray halo of Cen X-3 during its binary eclipse with the ASCA solid-state imaging spectrometer (SIS). The surface brightness profile (SBP) of the image in the low-energy band (0.5-3 keV) lies substantially above the point-spread function (PSF) of the X-ray telescope, while the SBP in the high-energy band (5-10 keV) exhibits no significant deviation. By contrast, the SBPs of Vela X-1 during its eclipse are consistent with the PSF in both the low- and high-energy bands -- strong evidence that a dust halo is indeed present in Cen X-3. Accordingly, we modeled the SBP of Cen X-3 taken from six consecutive time segments under the principal assumptions that the dust is distributed uniformly along a segment of the line of sight, the grains have a power-law size distribution, and the low-energy source flux was the same function of orbital phase before as during our observation. The best-fit set of parameters included a grain density value of 1.3 g/cu cm, substanially less than the density of 'astronomical silicate.' This result supports the idea that interstellar grains are 'fluffy' aggregates of smaller solid particles. We attribute the failure to detect a halo of Vela X-1 during its eclipse phase to extended strong circumsource absorption that probably occurred before the eclipse and allowed the halo to decay away before the observation began.
Free-radical probes for functional in vivo EPR imaging
NASA Astrophysics Data System (ADS)
Subramanian, S.; Krishna, M. C.
2007-02-01
Electron paramagnetic resonance imaging (EPRI) is one of the recent functional imaging modalities that can provide valuable in vivo physiological information on its own merit and aids as a complimentary imaging technique to MRI and PET of tissues especially with respect to in vivo pO II (oxygen partial pressure), redox status and pharmacology. EPR imaging mainly deals with the measurement of distribution and in vivo dynamics and redox changes using special nontoxic paramagnetic spin probes that can be infused into the object of investigation. These spin probes should be characterized by simple EPR spectra, preferably with narrow EPR lines. The line width should be reversibly sensitive to the concentration of in vivo pO II with a linear dependence. Several non-toxic paramagnetic probes, some particulate and insoluble and others water-soluble and infusible (by intravenous or intramuscular injection) have been developed which can be effectively used to quantitatively assess tissue redox status, and tumor hypoxia. Quantitative assessment of the redox status of tissue in vivo is important in investigating oxidative stress, and that of tissue pO II is very important in radiation oncology. Other areas in which EPR imaging and oxymetry may help are in the investigation of tumorangiogenesis, wound healing, oxygenation of tumor tissue by the ingestion of oxygen-rich gases, etc. The correct choice of the spin probe will depend on the modality of measurement (whether by CW or time-domain EPR imaging) and the particular physiology interrogated. Examples of the available spin probes and some EPR imaging applications employing them are presented.
X-band inverse class-F GaN internally-matched power amplifier
NASA Astrophysics Data System (ADS)
Zhao, Bo-Chao; Lu, Yang; Han, Wen-Zhe; Zheng, Jia-Xin; Zhang, Heng-Shuang; Ma, Pei-jun; Ma, Xiao-Hua; Hao, Yue
2016-09-01
An X-band inverse class-F power amplifier is realized by a 1-mm AlGaN/GaN high electron mobility transistor (HEMT). The intrinsic and parasitic components inside the transistor, especially output capacitor Cds, influence the harmonic impedance heavily at the X-band, so compensation design is used for meeting the harmonic condition of inverse class-F on the current source plane. Experiment results show that, in the continuous-wave mode, the power amplifier achieves 61.7% power added efficiency (PAE), which is 16.3% higher than the class-AB power amplifier realized by the same kind of HEMT. To the best of our knowledge, this is the first inverse class-F GaN internally-matched power amplifier, and the PAE is quite high at the X-band. Project supported by the National High Technology Research and Development Program of China (Grant No. 2015AA016801).
EPR-based material modelling of soils
NASA Astrophysics Data System (ADS)
Faramarzi, Asaad; Alani, Amir M.
2013-04-01
In the past few decades, as a result of the rapid developments in computational software and hardware, alternative computer aided pattern recognition approaches have been introduced to modelling many engineering problems, including constitutive modelling of materials. The main idea behind pattern recognition systems is that they learn adaptively from experience and extract various discriminants, each appropriate for its purpose. In this work an approach is presented for developing material models for soils based on evolutionary polynomial regression (EPR). EPR is a recently developed hybrid data mining technique that searches for structured mathematical equations (representing the behaviour of a system) using genetic algorithm and the least squares method. Stress-strain data from triaxial tests are used to train and develop EPR-based material models for soil. The developed models are compared with some of the well-known conventional material models and it is shown that EPR-based models can provide a better prediction for the behaviour of soils. The main benefits of using EPR-based material models are that it provides a unified approach to constitutive modelling of all materials (i.e., all aspects of material behaviour can be implemented within a unified environment of an EPR model); it does not require any arbitrary choice of constitutive (mathematical) models. In EPR-based material models there are no material parameters to be identified. As the model is trained directly from experimental data therefore, EPR-based material models are the shortest route from experimental research (data) to numerical modelling. Another advantage of EPR-based constitutive model is that as more experimental data become available, the quality of the EPR prediction can be improved by learning from the additional data, and therefore, the EPR model can become more effective and robust. The developed EPR-based material models can be incorporated in finite element (FE) analysis.
EPR/PTFE dosimetry for test reactor environments
DOE Office of Scientific and Technical Information (OSTI.GOV)
Vehar, D.W.; Griffin, P.J.; Quirk, T.J.
2011-07-01
The use of Electron Paramagnetic Resonance (EPR) spectroscopy with materials such as alanine is well established as a technique for measurement of ionizing radiation absorbed dose in photon and electron fields such as Co-60, high-energy bremsstrahlung and electron-beam fields [1]. In fact, EPR/Alanine dosimetry has become a routine transfer standard for national standards bodies such as NIST and NPL. In 1992 the Radiation Metrology Laboratory (RML) at Sandia National Laboratories implemented EPR/Alanine capabilities for use in routine and calibration activities at its Co-60 and pulsed-power facilities. At that time it also investigated the usefulness of the system for measurement ofmore » absorbed dose in the mixed neutron/photon environments of reactors such as the Sandia Pulsed Reactor and the Annular Core Research Reactor used for hardness testing of electronics. The RML concluded that the neutron response of alanine was a sufficiently high fraction of the overall dosimeter response that the resulting uncertainties in the photon dose would be unacceptably large for silicon-device testing. However, it also suggested that non-hydrogenous materials such as polytetrafluoroethylene (PTFE) would exhibit smaller neutron response and might be useful in mixed environments. Preliminary research with PTFE in photon environments indicated considerable promise, but further development was not pursued at that time. Because of renewed interest in absorbed dose measurements that could better define the individual contributions of photon and neutron components to the overall dose delivered to a test object, the RML has re-initiated the development of an EPR/PTFE dosimetry system. This effort consists of three stages: 1) Identification of PTFE materials that may be suitable for dosimetry applications. It was speculated that the inconsistency of EPR signatures in the earlier samples may have been due to variability in PTFE manufacturing processes. 2) Characterization of
Self-testing through EPR-steering
NASA Astrophysics Data System (ADS)
Šupić, Ivan; Hoban, Matty J.
2016-07-01
The verification of quantum devices is an important aspect of quantum information, especially with the emergence of more advanced experimental implementations of quantum computation and secure communication. Within this, the theory of device-independent robust self-testing via Bell tests has reached a level of maturity now that many quantum states and measurements can be verified without direct access to the quantum systems: interaction with the devices is solely classical. However, the requirements for this robust level of verification are daunting and require high levels of experimental accuracy. In this paper we discuss the possibility of self-testing where we only have direct access to one part of the quantum device. This motivates the study of self-testing via EPR-steering, an intermediate form of entanglement verification between full state tomography and Bell tests. Quantum non-locality implies EPR-steering so results in the former can apply in the latter, but we ask what advantages may be gleaned from the latter over the former given that one can do partial state tomography? We show that in the case of self-testing a maximally entangled two-qubit state, or ebit, EPR-steering allows for simpler analysis and better error tolerance than in the case of full device-independence. On the other hand, this improvement is only a constant improvement and (up to constants) is the best one can hope for. Finally, we indicate that the main advantage in self-testing based on EPR-steering could be in the case of self-testing multi-partite quantum states and measurements. For example, it may be easier to establish a tensor product structure for a particular party’s Hilbert space even if we do not have access to their part of the global quantum system.
Theoretical band structure of the superconducting antiperovskite oxide Sr3-xSnO
NASA Astrophysics Data System (ADS)
Ikeda, Atsutoshi; Fukumoto, Toshiyuki; Oudah, Mohamed; Hausmann, Jan Niklas; Yonezawa, Shingo; Kobayashi, Shingo; Sato, Masatoshi; Tassel, Cédric; Takeiri, Fumitaka; Takatsu, Hiroshi; Kageyama, Hiroshi; Maeno, Yoshiteru
2018-05-01
In order to investigate the position of the strontium deficiency in superconductive Sr3-xSnO, we synthesized and measured X-ray-diffraction patterns of Sr3-xSnO (x ∼ 0.5). Because no clear peaks originating from superstructures were observed, strontium deficiency is most likely to be randomly distributed. We also performed first-principles band-structure calculations on Sr3-xSnO (x = 0, 0.5) using two methods: full-potential linearized-augmented plane-wave plus local orbitals method and the Korringa-Kohn-Rostoker Green function method combined with the coherent potential approximation. We revealed that the Fermi energy of Sr3-xSnO in case of x ∼ 0.5 is about 0.8 eV below the original Fermi energy of the stoichiometric Sr3SnO, where the mixing of the valence p and conduction d orbitals are considered to be small.
NASA Astrophysics Data System (ADS)
Fukuda, Masahiro; Watanabe, Kazuhiro; Sakashita, Mitsuo; Kurosawa, Masashi; Nakatsuka, Osamu; Zaima, Shigeaki
2017-10-01
The energy band alignment of Ge1-xSnx/Ge1-x-ySixSny heterostructures was investigated, and control of the valence band offset at the Ge1-xSnx/Ge1-x-ySixSny heterointerface was achieved by controlling the Si and Sn contents in the Ge1-x-ySixSny layer. The valence band offset in the Ge0.902Sn0.098/Ge0.41Si0.50Sn0.09 heterostructure was evaluated to be as high as 330 meV, and its conduction band offset was estimated to be 150 meV by considering the energy bandgap calculated from the theoretical prediction. In addition, the formation of the strain-relaxed Ge1-x-ySixSny layer was examined and the crystalline structure was characterized. The epitaxial growth of a strain-relaxed Ge0.64Si0.21Sn0.15 layer with the degree of strain relaxation of 55% was examined using a virtual Ge substrate. Moreover, enhancement of the strain relaxation was demonstrated by post-deposition annealing, where a degree of strain relaxation of 70% was achieved after annealing at 400 °C. These results indicate the possibility for enhancing the indirect-direct crossover with a strained and high-Sn-content Ge1-xSnx layer on a strain-relaxed Ge1-x-ySixSny layer, realizing preferable carrier confinement by type-I energy band alignment with high conduction and valence band offsets.
Visible-light absorption and large band-gap bowing of GaN 1-xSb x from first principles
Sheetz, R. Michael; Richter, Ernst; Andriotis, Antonis N.; ...
2011-08-01
Applicability of the Ga(Sb x)N 1-x alloys for practical realization of photoelectrochemical water splitting is investigated using first-principles density functional theory incorporating the local density approximation and generalized gradient approximation plus the Hubbard U parameter formalism. Our calculations reveal that a relatively small concentration of Sb impurities is sufficient to achieve a significant narrowing of the band gap, enabling absorption of visible light. Theoretical results predict that Ga(Sb x)N 1-x alloys with 2-eV band gaps straddle the potential window at moderate to low pH values, thus indicating that dilute Ga(Sb x)N 1-x alloys could be potential candidates for splitting watermore » under visible light irradiation.« less
NASA Astrophysics Data System (ADS)
Bitar, Z.; El-Said Bakeer, D.; Awad, R.
2017-07-01
Zinc Cobalt nano ferrite doped with Praseodymium, Zn0.5Co0.5Fe2-xPrxO4 (0 ≤ x ≤ 0.2), were prepared by co-precipitation method from an aqueous solution containing metal chlorides and two concentrations of poly(vinylpyrrolidone) (PVP) 0 and 30g/L as capping agent. The samples were characterized using X-ray powder diffraction (XRD), Transmission Electron Microscope (TEM), UV-visible optical spectroscopy, Fourier transform infrared (FTIR) and Electron Paramagnetic Resonance (EPR). XRD results display the formation of cubic spinel structure with space group Fd3m and the lattice parameter (a) is slightly decreased for PVP capping samples. The particle size that determined by TEM, decreases for PVP capping samples. The optical band energy Eg increases for PVP capping samples, confirming the variation of energy gap with the particle size. The FTIR results indicate that the metal oxide bands were shifted for the PVP capping samples. EPR data shows that the PVP addition increases the magnetic resonance field and hence decreases the g-factor.
Hu, Rongwei; Mun, Eun Deok; Altarawneh, M. M.; ...
2012-02-13
The upper critical fields H c2(T) of single crystals of Sr 1-xEu x(Fe₀.₈₉Co₀.₁₁)₂As₂ (x=0.20 and 0.46) were determined by radio-frequency penetration depth measurements in pulsed magnetic fields. H c2(T) approaches the Pauli limiting field but shows an upward curvature with an enhancement from the orbital limited field, as inferred from the Werthamer-Helfand-Hohenberg theory. We discuss the temperature dependence of the upper critical fields and the decreasing anisotropy using a two-band BCS model.
Investigation of radical locations in various sesame seeds by CW EPR and 9-GHz EPR imaging.
Nakagawa, K; Hara, H
2015-01-01
We investigated the location of radical in various sesame seeds using continuous-wave (CW) electron paramagnetic resonance (EPR) and 9-GHz EPR imaging. CW EPR detected persistent radicals (single line) for various sesame seeds. The EPR linewidth of black sesame seeds was narrower than that of the irradiated white sesame seeds. A very small signal was detected for the white sesame seeds. Two-dimensional (2D) imaging using a 9-GHz EPR imager showed that radical locations vary for various sesame seeds. The paramagnetic species in black sesame seeds were located on the seed coat (skin) and in the hilum region. The signal with the highest intensity was obtained from the hilum part. A very low-intensity image was observed for the white sesame seeds. In addition, the 2D imaging of the irradiated white sesame seeds showed that free radicals were located throughout the entire seed. For the first time, CW EPR and 9-GHz EPR imaging showed the exact location of radical species in various sesame seeds.
Multichannel X-Band Dielectric-Resonator Oscillator
NASA Technical Reports Server (NTRS)
Mysoor, Narayan; Dennis, Matthew; Cook, Brian
2006-01-01
A multichannel dielectric-resonator oscillator (DRO), built as a prototype of a local oscillator for an X-band transmitter or receiver, is capable of being electrically tuned among and within 26 adjacent frequency channels, each 1.16 MHz wide, in a band ranging from 7,040 to 7,070 GHz. The tunability of this oscillator is what sets it apart from other DROs, making it possible to use mass-produced oscillator units of identical design in diverse X-band applications in which there are requirements to use different fixed frequencies or to switch among frequency channels. The oscillator (see figure) includes a custom-designed voltage-controlled-oscillator (VCO) monolithic microwave integrated circuit (MMIC), a dielectric resonator disk (puck), and two varactor-coupling circuits, all laid out on a 25-mil (0.635-mm)-thick alumina substrate having a length and width of 17.8 mm. The resonator disk has a diameter of 8.89 mm and a thickness of 4.01 mm. The oscillator is mounted in an 8.9-mm-deep cavity in a metal housing. The VCO MMIC incorporates a negative- resistance oscillator amplifier along with a buffer amplifier. The resonator disk is coupled to a microstrip transmission line connected to the negative-resistance port of the VCO MMIC. The two varactor-coupling circuits include microstrip lines, laid out orthogonally to each other, for coupling with the resonator disk. Each varactor microstrip line is DC-coupled to an external port via a microwave choke. One varactor is used for coarse tuning to select a channel; the other varactor is used (1) for fine tuning across the 1.16-MHz width of each channel and (2) as a feedback port for a phase-lock loop. The resonator disk is positioned to obtain (1) the most desirable bandwidth, (2) relatively tight coupling with the microstrip connected to the coarse-tuning varactor, and (3) relatively loose coupling with the microstrip connected to the fine-tuning varactor. Measurements of performance showed that the oscillator can be
Active cancellation - A means to zero dead-time pulse EPR.
Franck, John M; Barnes, Ryan P; Keller, Timothy J; Kaufmann, Thomas; Han, Songi
2015-12-01
The necessary resonator employed in pulse electron paramagnetic resonance (EPR) rings after the excitation pulse and creates a finite detector dead-time that ultimately prevents the detection of signal from fast relaxing spin systems, hindering the application of pulse EPR to room temperature measurements of interesting chemical or biological systems. We employ a recently available high bandwidth arbitrary waveform generator (AWG) to produce a cancellation pulse that precisely destructively interferes with the resonant cavity ring-down. We find that we can faithfully detect EPR signal at all times immediately after, as well as during, the excitation pulse. This is a proof of concept study showcasing the capability of AWG pulses to precisely cancel out the resonator ring-down, and allow for the detection of EPR signal during the pulse itself, as well as the dead-time of the resonator. However, the applicability of this approach to conventional EPR experiments is not immediate, as it hinges on either (1) the availability of low-noise microwave sources and amplifiers to produce the necessary power for pulse EPR experiment or (2) the availability of very high conversion factor micro coil resonators that allow for pulse EPR experiments at modest microwave power. Copyright © 2015 Elsevier Inc. All rights reserved.
Kavalenka, Aleh; Urbančič, Iztok; Belle, Valérie; Rouger, Sabrina; Costanzo, Stéphanie; Kure, Sandra; Fournel, André; Longhi, Sonia; Guigliarelli, Bruno; Strancar, Janez
2010-01-01
To characterize the structure of dynamic protein systems, such as partly disordered protein complexes, we propose a novel approach that relies on a combination of site-directed spin-labeled electron paramagnetic resonance spectroscopy and modeling of local rotation conformational spaces. We applied this approach to the intrinsically disordered C-terminal domain of the measles virus nucleoprotein (NTAIL) both free and in complex with the X domain (XD, aa 459–507) of the viral phosphoprotein. By comparing measured and modeled temperature-dependent restrictions of the side-chain conformational spaces of 12 SL cysteine-substituted NTAIL variants, we showed that the 490–500 region of NTAIL is prestructured in the absence of the partner, and were able to quantitatively estimate, for the first time to our knowledge, the extent of the α-helical sampling of the free form. In addition, we showed that the 505–525 region of NTAIL conserves a significant degree of freedom even in the bound form. The latter two findings provide a mechanistic explanation for the reported rather high affinity of the NTAIL-XD binding reaction. Due to the nanosecond timescale of X-band EPR spectroscopy, we were also able to monitor the disordering in the 488–525 region of NTAIL, in particular the unfolding of the α-helical region when the temperature was increased from 281 K to 310 K. PMID:20303863
An X-Band SOS Resistive Gate-Insulator-Semiconductor /RIS/ switch
NASA Astrophysics Data System (ADS)
Kwok, S. P.
1980-02-01
The new X-Band Resistive Gate-Insulator-Semiconductor (RIS) switch has been fabricated on silicon-on-sapphire, and its equivalent circuit model characterized. An RIS SPST switch with 20-dB on/off isolation, 1.2-dB insertion loss, and power handling capacity in excess of 20-W peak has been achieved at X band. The device switching time is on the order of 600 ns, and it requires negligible control holding current in both on and off states. The device is compatible with monolithic integrated-circuit technology and thus is suitable for integration into low-cost monolithic phase shifters or other microwave integrated circuits.
Combined multifrequency EPR and DFT study of dangling bonds in a-Si:H
NASA Astrophysics Data System (ADS)
Fehr, M.; Schnegg, A.; Rech, B.; Lips, K.; Astakhov, O.; Finger, F.; Pfanner, G.; Freysoldt, C.; Neugebauer, J.; Bittl, R.; Teutloff, C.
2011-12-01
Multifrequency pulsed electron paramagnetic resonance (EPR) spectroscopy using S-, X-, Q-, and W-band frequencies (3.6, 9.7, 34, and 94 GHz, respectively) was employed to study paramagnetic coordination defects in undoped hydrogenated amorphous silicon (a-Si:H). The improved spectral resolution at high magnetic field reveals a rhombic splitting of the g tensor with the following principal values: gx=2.0079, gy=2.0061, and gz=2.0034, and shows pronounced g strain, i.e., the principal values are widely distributed. The multifrequency approach furthermore yields precise 29Si hyperfine data. Density functional theory (DFT) calculations on 26 computer-generated a-Si:H dangling-bond models yielded g values close to the experimental data but deviating hyperfine interaction values. We show that paramagnetic coordination defects in a-Si:H are more delocalized than computer-generated dangling-bond defects and discuss models to explain this discrepancy.
NASA Astrophysics Data System (ADS)
Azza, Gorrab; Zribi, Mehrez; Baghdadi, Nicolas; Mougenot, Bernard; Boulet, Gilles; Lili-Chabaane, Zohra
2015-04-01
Mapping surface soil moisture with meter-scale spatial resolution is appropriate for multi- domains particularly hydrology and agronomy. It allows water resources and irrigation management decisions, drought monitoring and validation of multi-hydrological water balance models. In the last years, various studies have demonstrated the large potential of radar remote sensing data, mainly from C frequency band, to retrieve soil moisture. However, the accuracy of the soil moisture estimation, by inversing backscattering radar coefficients (σ°), is affected by the influence of surface roughness and vegetation biomass contributions. In recent years, different empirical, semi empirical and physical approaches are developed for bare soil conditions, to estimate accurately spatial soil moisture variability. In this study, we propose an approach based on the change detection method for the retrieval of surface soil moisture at a higher spatial resolution. The proposal algorithm combines multi-temporal X-band SAR images (TerraSAR-X) with different continuous thetaprobe measurements. Seven thetaprobe stations are installed at different depths over the central semi arid region of Tunisia (9°23' - 10°17' E, 35° 1'-35°55' N). They cover approximately the entire of our study site and provide regional scale information. Ground data were collected over agricultural bare soil fields simultaneously to various TerraSAR-X data acquired during 2013-2014 and 2014-2015. More than fourteen test fields were selected for each spatial acquisition campaign, with variations in soil texture and in surface soil roughness. For each date, we considered the volumetric water content with thetaprobe instrument and gravimetric sampling; we measured also the roughness parameters with pin profilor. To retrieve soil moisture from X-band SAR data, we analyzed statistically the sensitivity between radar measurements and ground soil moisture derived from permanent thetaprobe stations. Our analyses are
Playback system designed for X-Band SAR
NASA Astrophysics Data System (ADS)
Yuquan, Liu; Changyong, Dou
2014-03-01
SAR(Synthetic Aperture Radar) has extensive application because it is daylight and weather independent. In particular, X-Band SAR strip map, designed by Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, provides high ground resolution images, at the same time it has a large spatial coverage and a short acquisition time, so it is promising in multi-applications. When sudden disaster comes, the emergency situation acquires radar signal data and image as soon as possible, in order to take action to reduce loss and save lives in the first time. This paper summarizes a type of X-Band SAR playback processing system designed for disaster response and scientific needs. It describes SAR data workflow includes the payload data transmission and reception process. Playback processing system completes signal analysis on the original data, providing SAR level 0 products and quick image. Gigabit network promises radar signal transmission efficiency from recorder to calculation unit. Multi-thread parallel computing and ping pong operation can ensure computation speed. Through gigabit network, multi-thread parallel computing and ping pong operation, high speed data transmission and processing meet the SAR radar data playback real time requirement.
NASA Astrophysics Data System (ADS)
da Silva Rocha Paz, Igor; Ichiba, Abdellah; Skouri-Plakali, Ilektra; Lee, Jisun; Gires, Auguste; Tchiguirinskaia, Ioulia; Schertzer, Daniel
2017-04-01
Climate change and global warming are expected to make precipitation events more frequent, more severe and more local. This may have serious consequences for human health, the environment, cultural heritage, economic activities, utilities and public service providers. Then precipitation risk and water management is a key challenge for densely populated urban areas. Applications derived from high (time and space) resolution observation of precipitations are to make our cities more weather-ready. Finer resolution data available from X-band dual radar measurements enhance engineering tools as used for urban planning policies as well as protection (mitigation/adaptation) strategies to tackle climate-change related weather events. For decades engineering tools have been developed to work conveniently either with very local rain gauge networks, or with mainly C-band weather radars that have gradually been set up for space-time remote sensing of precipitation. Most of the time, the C-band weather radars continue to be calibrated by the existing rain gauge networks. Inhomogeneous distributions of rain gauging networks lead to only a partial information on the rainfall fields. In fact, the statistics of measured rainfall is strongly biased by the fractality of the measuring networks. This fractality needs to be properly taken in to account to retrieve the original properties of the rainfall fields, in spite of the radar data calibration. In this presentation, with the help of multifractal analysis, we first demonstrate that the semi-distributed hydrological models statistically reduce the rainfall fields into rainfall measured by a much scarcer network of virtual rain gauges. For this purpose, we use C-band and X-band radar data. The first has a resolution of 1 km in space and 5 min in time and is in fact a product provided by RHEA SAS after treating the Météo-France C-band radar data. The latter is measured by the radar operated at Ecole des Ponts and has a resolution of
An Improved X-Band Maser System for Deep Space Network Applications
NASA Astrophysics Data System (ADS)
Britcliffe, M.; Hanson, T.; Fernandez, J.
2000-01-01
An 8450-MHz (X-band) maser system utilizing a commercial Gifford--McMahon (GM) closed-cycle cryocooler (CCR) was designed, fabricated, and demonstrated. The CCR system was used to cool a maser operating at 8450 MHz. The prototype GM CCR system meets or exceeds all Deep Space Network requirements for maser performance. The two-stage GM CCR operates at 4.2 K; for comparison, the DSN's current three-stage cryocooler, which uses a Joule--Thompson cooling stage in addition to GM cooling, operates at 4.5 K. The new CCR withstands heat loads of 1.5 W at 4.2 K as compared to 1 W at 4.5 K for the existing DSN cryocooler used for cooling masers. The measured noise temperature, T_e, of the maser used for these tests is defined at the ambient connection to the antenna feed system. The T_e measured 5.0 K at a CCR temperature of 4.5 K, about 1.5 K higher than the noise temperature of a typical DSN Block II-A X-band traveling-wave maser (TWM). Reducing the temperature of the CCR significantly lowers the maser noise temperature and increases maser gain and bandwidth. The new GM CCR gives future maser systems significant operational advantages, including reduced maintenance time and logistics requirements. The results of a demonstration of this new system are presented. Advantages of using a GM-cooled maser and the effects of the reduced CCR temperature on maser performance are discussed.
NASA Astrophysics Data System (ADS)
Lavrentyev, A. A.; Gabrelian, B. V.; Vu, V. T.; Ananchenko, L. N.; Isaenko, L. I.; Yelisseyev, A. P.; Khyzhun, O. Y.
2017-04-01
We report on measurements of X-ray photoelectron (XP) spectra for pristine and Ar+ ion-irradiated surfaces of LiGaSe2 single crystal grown by Bridgman-Stockbarger method. Electronic structure of the LiGaSe2 compound is studied from a theoretical and experimental viewpoint. In particular, total and partial densities of states of LiGaSe2 are investigated by density functional theory (DFT) calculations employing the augmented plane wave + local orbitals (APW + lo) method and they are verified by data of X-ray spectroscopy measurements. The DFT calculations indicate that the main contributors to the valence band of LiGaSe2 are the Se 4p states, which contribute mainly at the top and in the upper portion of the valence band, with also essential contributions of these states in the lower portion of the band. Other substantial contributions to the valence band of LiGaSe2 emerge from the Ga 4s and Ga 4p states contributing mainly at the lower ant upper portions of the valence band, respectively. With respect to the conduction band, the calculations indicate that its bottom is composed mainly from contributions of the unoccupied Ga s and Se p states. The present calculations are confirmed experimentally when comparing the XP valence-band spectrum of the LiGaS2 single crystal on a common energy scale with the X-ray emission bands representing the energy distribution of the Ga 4p and Se 4p states. Measurements of the fundamental absorption edges at room temperature reveal that bandgap value, Eg, of LiGaSe2 is equal to 3.47 eV and the Eg value increases up to 3.66 eV when decreasing temperature to 80 K. The main optical characteristics of the LiGaSe2 compound are clarified by the DFT calculations.
NASA Astrophysics Data System (ADS)
Gunn, Grant; Duguay, Claude; Atwood, Don
2017-04-01
This study identifies the dominant scattering mechanism for C-, X- and Ku-band for bubbled freshwater lake ice in the Hudson Bay Lowlands near Churchill, Canada, using a winter time series of fully polarimetric ground-based (X- and Ku-band, UW-Scat) scatterometer and spaceborne (C-band) synthetic aperture radar (SAR, Radarsat-2) observations collected coincidentally to in-situ snow and ice measurements. Scatterometer observations identify two dominant backscatter sources from the ice cover: the snow-ice, and ice-water interface. Using in-situ measurements as ground-truth, a winter time series of scatterometer and satellite acquisitions show increases in backscatter from the ice-water interface prior to the timing of tubular bubble development in the ice cover. This timing indicates that scattering in the ice is independent of double-bounce scatter caused by tubular bubble inclusions. Concurrently, the co-polarized phase difference of interactions at the ice-water interface from both scatterometer and SAR observations are centred at 0° throughout the time series, indicating a scattering regime other than double bounce. A Yamaguchi three-component decomposition of SAR observations is presented for C-band acquisitions indicating a dominant single-bounce scattering mechanism regime, which is hypothesized to be a result of an ice-water interface that presents a rough surface or a surface composed of preferentially oriented facets. This study is the first to present a winter time series of coincident ground-based and spaceborne fully polarimetric active microwave observations for bubbled freshwater lake ice.
2013-03-08
tions in the studied SLS structures . The fit of the dependence of the valence- band energy of unstrained InAs1!xSbx on the composition x with a... band . STRUCTURES Bulk InAsSb epilayers on metamorphic buffers and InAsSb/InAs strained-layer superlattices (SLS) were grown on GaSb substrates by solid...meV in InAs and Ev = 0 meV in InSb. For InAsSb with 22.5% Sb grown on GaSb , an unstrained valence- band energy of Ev = !457 meV was obtained. For the
Lithium formate for EPR dosimetry: radiation-induced radical trapping at low temperatures.
Krivokapić, André; Aalbergsjø, Siv G; De Cooman, Hendrik; Hole, Eli Olaug; Nelson, William H; Sagstuen, Einar
2014-05-01
Radiation-induced primary radicals in lithium formate. A material used in EPR dosimetry have been studied using electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR) and ENDOR-Induced EPR (EIE) techniques. In this study, single crystals were X irradiated at 6-8 K and radical formation at these and higher temperatures were investigated. Periodic density functional theory calculations were used to assist in assigning the radical structures. Mainly two radicals are present at 6 K, the well-known CO2(•-) radical and a protonated electron-gain product. Hyperfine coupling tensors for proton and lithium interactions were obtained for these two radicals and show that the latter radical exists in four conformations with various degrees of bending at the radical center. Pairs of CO2(•-) radicals were also observed and the tensor for the electron-electron dipolar coupling was determined for the strongest coupled pair, which exhibited the largest spectral intensity. Upon warming, both the radical pairs and the reduction product decay, the latter apparently by a transient species. Above 200 K the EPR spectrum was mainly due to the CO2(•-) (mono) radicals, which were previously characterized as the dominant species present at room temperature and which account for the dosimetric EPR signal.
Multicolor emission from intermediate band semiconductor ZnO 1-xSe x
DOE Office of Scientific and Technical Information (OSTI.GOV)
Welna, M.; Baranowski, M.; Linhart, W. M.
Photoluminescence and photomodulated reflectivity measurements of ZnOSe alloys are used to demonstrate a splitting of the valence band due to the band anticrossing interaction between localized Se states and the extended valence band states of the host ZnO matrix. A strong multiband emission associated with optical transitions from the conduction band to lower E - and upper E + valence subbands has been observed at room temperature. The composition dependence of the optical transition energies is well explained by the electronic band structure calculated using the kp method combined with the band anticrossing model. The observation of the multiband emissionmore » is possible because of relatively long recombination lifetimes. Longer than 1 ns lifetimes for holes photoexcited to the lower valence subband offer a potential of using the alloy as an intermediate band semiconductor for solar power conversion applications.« less
Multicolor emission from intermediate band semiconductor ZnO 1-xSe x
Welna, M.; Baranowski, M.; Linhart, W. M.; ...
2017-03-13
Photoluminescence and photomodulated reflectivity measurements of ZnOSe alloys are used to demonstrate a splitting of the valence band due to the band anticrossing interaction between localized Se states and the extended valence band states of the host ZnO matrix. A strong multiband emission associated with optical transitions from the conduction band to lower E - and upper E + valence subbands has been observed at room temperature. The composition dependence of the optical transition energies is well explained by the electronic band structure calculated using the kp method combined with the band anticrossing model. The observation of the multiband emissionmore » is possible because of relatively long recombination lifetimes. Longer than 1 ns lifetimes for holes photoexcited to the lower valence subband offer a potential of using the alloy as an intermediate band semiconductor for solar power conversion applications.« less
Yan, Baojun; Liu, Shulin; Heng, Yuekun; Yang, Yuzhen; Yu, Yang; Wen, Kaile
2017-12-01
Pure aluminum oxide (Al 2 O 3 ) and zinc aluminum oxide (Zn x Al 1-x O) thin films were deposited by atomic layer deposition (ALD). The microstructure and optical band gaps (E g ) of the Zn x Al 1-x O (0.2 ≤ x ≤ 1) films were studied by X-ray diffractometer and Tauc method. The band offsets and alignment of atomic-layer-deposited Al 2 O 3 /Zn 0.8 Al 0.2 O heterojunction were investigated in detail using charge-corrected X-ray photoelectron spectroscopy. In this work, different methodologies were adopted to recover the actual position of the core levels in insulator materials which were easily affected by differential charging phenomena. Valence band offset (ΔE V ) and conduction band offset (ΔE C ) for the interface of the Al 2 O 3 /Zn 0.8 Al 0.2 O heterojunction have been constructed. An accurate value of ΔE V = 0.82 ± 0.12 eV was obtained from various combinations of core levels of heterojunction with varied Al 2 O 3 thickness. Given the experimental E g of 6.8 eV for Al 2 O 3 and 5.29 eV for Zn 0.8 Al 0.2 O, a type-I heterojunction with a ΔE C of 0.69 ± 0.12 eV was found. The precise determination of the band alignment of Al 2 O 3 /Zn 0.8 Al 0.2 O heterojunction is of particular importance for gaining insight to the design of various electronic devices based on such heterointerface.
A hand-held EPR scanner for transcutaneous oximetry
NASA Astrophysics Data System (ADS)
Wolfson, Helen; Ahmad, Rizwan; Twig, Ygal; Blank, Aharon; Kuppusamy, Periannan
2015-03-01
Cutaneous (skin) oxygenation is an important prognostic factor for the treatment of chronic wounds, skin cancer, diabetes side effects, and limb amputation. Currently, there are no reliable methods for measuring this parameter. Oximetry, using electron paramagnetic resonance (EPR) spectroscopy, is emerging as a potential tool for clinical oximetry, including cutaneous applications. The problem with EPR oximetry, however, is that the conventional EPR design requires the use of a large magnet that can generate homogeneous field across the sample, making it unattractive for clinical practice. We present a novel approach that makes use of a miniature permanent magnet, combined with a small microwave resonator, to enable the acquisition of EPR signals from paramagnetic species placed on the skin. The instrumentation consists of a hand-held, modular, cylindrical probehead with overall dimensions of 36-mm diameter and 24-mm height, with 150-g weight. The probehead includes a Halbach array of 16 pieces (4×4×8 mm3) of Sm-Co permanent magnet and a loop-gap resonator (2.24 GHz). Preliminary measurements using a Hahn-echo pulse sequence (800 echos in 20 ms) showed a signalto- noise ratio of ~70 compared to ~435 in a homogenous magnet under identical settings. Further work is in progress to improve the performance of the probehead and to optimize the hand-held system for clinical use
A model for the energy band gap of GaSbxAs1-x and InSbxAs1-x in the whole composition range
NASA Astrophysics Data System (ADS)
Zhao, Chuan-Zhen; Ren, He-Yu; Wei, Tong; Wang, Sha-Sha; Wang, Jun
2018-04-01
The band gap evolutions of GaSbxAs1-x and InSbxAs1-x in the whole composition range are investigated. It is found that the band gap evolutions of GaSbxAs1-x and InSbxAs1-x are determined by two factors. One is the impurity-host interaction in the As-rich and Sb-rich composition ranges. The other is the intraband coupling within the conduction band and separately within the valence band in the moderate composition range. Based on the band gap evolutions of GaSbxAs1-x and InSbxAs1-x, a model is established. In addition, it is found that the impurity-host interaction is determined by not only the mismatches in size and electronegativity between the introduced atoms in the host material and the anions of the host material, but also the difference in electronegativity between the introduced atoms in the host material and the cations of the host material.
NASA Technical Reports Server (NTRS)
Evans, Diane L. (Editor); Plaut, Jeffrey (Editor)
1996-01-01
The Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar (SIR-C/X-SAR) is the most advanced imaging radar system to fly in Earth orbit. Carried in the cargo bay of the Space Shuttle Endeavour in April and October of 1994, SIR-C/X-SAR simultaneously recorded SAR data at three wavelengths (L-, C-, and X-bands; 23.5, 5.8, and 3.1 cm, respectively). The SIR-C/X-SAR Science Team consists of 53 investigator teams from more than a dozen countries. Science investigations were undertaken in the fields of ecology, hydrology, ecology, and oceanography. This report contains 44 investigator team reports and several additional reports from coinvestigators and other researchers.
Eaton, Sandra S; Shi, Yilin; Woodcock, Lukas; Buchanan, Laura A; McPeak, Joseph; Quine, Richard W; Rinard, George A; Epel, Boris; Halpern, Howard J; Eaton, Gareth R
2017-07-01
In rapid-scan EPR the magnetic field or frequency is repeatedly scanned through the spectrum at rates that are much faster than in conventional continuous wave EPR. The signal is directly-detected with a mixer at the source frequency. Rapid-scan EPR is particularly advantageous when the scan rate through resonance is fast relative to electron spin relaxation rates. In such scans, there may be oscillations on the trailing edge of the spectrum. These oscillations can be removed by mathematical deconvolution to recover the slow-scan absorption spectrum. In cases of inhomogeneous broadening, the oscillations may interfere destructively to the extent that they are not visible. The deconvolution can be used even when it is not required, so spectra can be obtained in which some portions of the spectrum are in the rapid-scan regime and some are not. The technology developed for rapid-scan EPR can be applied generally so long as spectra are obtained in the linear response region. The detection of the full spectrum in each scan, the ability to use higher microwave power without saturation, and the noise filtering inherent in coherent averaging results in substantial improvement in signal-to-noise relative to conventional continuous wave spectroscopy, which is particularly advantageous for low-frequency EPR imaging. This overview describes the principles of rapid-scan EPR and the hardware used to generate the spectra. Examples are provided of its application to imaging of nitroxide radicals, diradicals, and spin-trapped radicals at a Larmor frequency of ca. 250MHz. Copyright © 2017 Elsevier Inc. All rights reserved.
The Celestial Reference Frame at X/Ka-band (8.4/32 GHz)
NASA Technical Reports Server (NTRS)
Jacobs, C. S.; Clark, J. E.; Heflin, M. B.; Skjerve, L. J.; Sovers, O. J.; Garcia-Miro, C.; Moll, V. E.; Horiuchi, S.
2010-01-01
A celestial reference frame at X/Kaband (8.4/32 GHz) has been constructed using fiftyone 24-hour sessions with the Deep Space Network. We report on observations which have detected 436 sources covering the full 24 hours of right ascension and declinations down to -45 deg. Comparison of this X/Ka-band frame to the S/X-band (2.3/8.4 GHz) ICRF2 shows wRMS agreement of 200 micro-arcsec ( mu as) in alpha cos delta and 290 mu as in delta. There is evidence for zonal errors at the 100 mu as level. Known errors include limited SNR, lack of phase calibration, troposphere mismodelling, and limited southern geometry. The motivations for extending the ICRF to frequencies above 8 GHz are to access more compact source morphology for improved frame stability, to provide calibrators for phase referencing, and to support spacecraft navigation at Ka-band.
EPR oximetry in three spatial dimensions using sparse spin distribution
NASA Astrophysics Data System (ADS)
Som, Subhojit; Potter, Lee C.; Ahmad, Rizwan; Vikram, Deepti S.; Kuppusamy, Periannan
2008-08-01
A method is presented to use continuous wave electron paramagnetic resonance imaging for rapid measurement of oxygen partial pressure in three spatial dimensions. A particulate paramagnetic probe is employed to create a sparse distribution of spins in a volume of interest. Information encoding location and spectral linewidth is collected by varying the spatial orientation and strength of an applied magnetic gradient field. Data processing exploits the spatial sparseness of spins to detect voxels with nonzero spin and to estimate the spectral linewidth for those voxels. The parsimonious representation of spin locations and linewidths permits an order of magnitude reduction in data acquisition time, compared to four-dimensional tomographic reconstruction using traditional spectral-spatial imaging. The proposed oximetry method is experimentally demonstrated for a lithium octa- n-butoxy naphthalocyanine (LiNc-BuO) probe using an L-band EPR spectrometer.
NASA Technical Reports Server (NTRS)
Young, Steve; UijtdeHaag, Maarten; Sayre, Jonathon
2003-01-01
Synthetic Vision Systems (SVS) provide pilots with displays of stored geo-spatial data representing terrain, obstacles, and cultural features. As comprehensive validation is impractical, these databases typically have no quantifiable level of integrity. Further, updates to the databases may not be provided as changes occur. These issues limit the certification level and constrain the operational context of SVS for civil aviation. Previous work demonstrated the feasibility of using a realtime monitor to bound the integrity of Digital Elevation Models (DEMs) by using radar altimeter measurements during flight. This paper describes an extension of this concept to include X-band Weather Radar (WxR) measurements. This enables the monitor to detect additional classes of DEM errors and to reduce the exposure time associated with integrity threats. Feature extraction techniques are used along with a statistical assessment of similarity measures between the sensed and stored features that are detected. Recent flight-testing in the area around the Juneau, Alaska Airport (JNU) has resulted in a comprehensive set of sensor data that is being used to assess the feasibility of the proposed monitor technology. Initial results of this assessment are presented.
Spaced-antenna wind estimation using an X-band active phased-array weather radar
NASA Astrophysics Data System (ADS)
Venkatesh, Vijay
Over the past few decades, several single radar methods have been developed to probe the kinematic structure of storms. All these methods trade angular-resolution to retrieve the wind-field. To date, the spaced-antenna method has been employed for profiling the ionosphere and the precipitation free lower atmosphere. This work focuses on applying the spaced-antenna method on an X-band active phased-array radar for high resolution horizontal wind-field retrieval from precipitation echoes. The ability to segment the array face into multiple displaced apertures allows for flexible spaced-antenna implementations. The methodology employed herein comprises of Monte-Carlo simulations to optimize the spaced-antenna system design and analysis of real data collected with the designed phased-array system. The contribution that underpins this dissertation is the demonstration of qualitative agreement between spaced-antenna and Doppler beam swinging retrievals based on real data. First, simulations of backscattered electric fields at the antenna array elements are validated using theoretical expressions. Based on the simulations, the degrees of freedom in the spaced-antenna system design are optimized for retrieval of mean baseline wind. We show that the designed X-band spaced-antenna system has lower retrieval uncertainty than the existing S-band spaced-antenna implementation on the NWRT. This is because of the flexibility to synthesize small overlapping apertures and the ability to obtain statistically independent samples at a faster rate at X-band. We then demonstrate a technique to make relative phase-center displacement measurements based on simulations and real data from the phased-array spaced-antenna system. This simple method uses statistics of precipitation echoes and apriori beamwidth measurements to make field repeatable phase-center displacement measurements. Finally, we test the hypothesis that wind-field curvature effects are common to both the spaced-antenna and
Steering, Entanglement, Nonlocality, and the EPR Paradox
NASA Astrophysics Data System (ADS)
Wiseman, Howard; Jones, Steve; Andrew, Doherty
2007-06-01
The concept of steering was introduced by Schroedinger in 1935 as a generalization of the EPR paradox for arbitrary pure bipartite entangled states and arbitrary measurements by one party. Until now, it has never been rigorously defined, so it has not been known (for example) what mixed states are steerable (that is, can be used to exhibit steering). We provide an operational definition, from which we prove (by considering Werner states and Isotropic states) that steerable states are a strict subset of the entangled states, and a strict superset of the states that can exhibit Bell-nonlocality. For arbitrary bipartite Gaussian states we derive a linear matrix inequality that decides the question of steerability via Gaussian measurements, and we relate this to the original EPR paradox.
Advances in Probes and Methods for Clinical EPR Oximetry
Hou, Huagang; Khan, Nadeem; Jarvis, Lesley A.; Chen, Eunice Y.; Williams, Benjamin B.; Kuppusamy, Periannan
2015-01-01
EPR oximetry, which enables reliable, accurate, and repeated measurements of the partial pressure of oxygen in tissues, provides a unique opportunity to investigate the role of oxygen in the pathogenesis and treatment of several diseases including cancer, stroke, and heart failure. Building on significant advances in the in vivo application of EPR oximetry for small animal models of disease, we are developing suitable probes and instrumentation required for use in human subjects. Our laboratory has established the feasibility of clinical EPR oximetry in cancer patients using India ink, the only material presently approved for clinical use. We now are developing the next generation of probes, which are both superior in terms of oxygen sensitivity and biocompatibility including an excellent safety profile for use in humans. Further advances include the development of implantable oxygen sensors linked to an external coupling loop for measurements of deep-tissue oxygenations at any depth, overcoming the current limitation of 10 mm. This paper presents an overview of recent developments in our ability to make meaningful measurements of oxygen partial pressures in human subjects under clinical settings. PMID:24729217
Applications of EPR steering in quantum teleportation and NOON states
NASA Astrophysics Data System (ADS)
Zárate, Laura Rosales
2018-04-01
Einstein-Podolsky-Rosen (EPR) steering refers to the type of correlations described in the EPR paradox, where one observer seems to affect ("steer") the state of other observer by using local measurements. There have been several works regarding characterization and quantification of EPR steering. One characteristic of this non-local correlation is that it can be asymmetric, while entanglement is symmetric. This asymmetric property is relevant for potential applications of EPR steering to quantum information, in particular to quantum cryptography and quantum teleportation. This latter refers to the process where one observer sends an unknown quantum state to Bob, who is in a different location. They communicate by classical means. Here we will show that EPR steering is a necessary resource to obtain secure continuous variable teleportation. We will also consider NOON states, which is an example of an entangled state. For this state, we will present a steering signature. This contribution reviews the work derived in Refs. [1] and [2], which was presented as an invited talk in ELAF 2017.
X-band noise temperature effects of rain on DSN antenna feedhorns
NASA Technical Reports Server (NTRS)
Slobin, S. D.; Franco, M. M.; Clauss, R. C.
1982-01-01
Simulated rain tests were carried out to determine the noise temperature contribution of liquid water adhering to the aperture cover material on both a standard DSN X-band feedhorn and on an S/X-band common aperture feedhorn. It was found that for the particular common aperture feedhorn tested, system noise temperature increases were much greater when the plastic horn cover material was old and weathered than when it was new. The age and condition of the aperture cover material is believed to be a major factor in the amount of degradation experienced by a telecommunications system during rain events.
Wormhole and entanglement (non-)detection in the ER=EPR correspondence
Bao, Ning; Pollack, Jason; Remmen, Grant N.
2015-11-19
The recently proposed ER=EPR correspondence postulates the existence of wormholes (Einstein-Rosen bridges) between entangled states (such as EPR pairs). Entanglement is famously known to be unobservable in quantum mechanics, in that there exists no observable (or, equivalently, projector) that can accurately pick out whether a generic state is entangled. Many features of the geometry of spacetime, however, are observables, so one might worry that the presence or absence of a wormhole could identify an entangled state in ER=EPR, violating quantum mechanics, specifically, the property of state-independence of observables. In this note, we establish that this cannot occur: there is nomore » measurement in general relativity that unambiguously detects the presence of a generic wormhole geometry. Furthermore, this statement is the ER=EPR dual of the undetectability of entanglement.« less
Sleuthing the MSL EDL performance from an X band carrier perspective
NASA Astrophysics Data System (ADS)
Oudrhiri, Kamal; Asmar, Sami; Estabrook, Polly; Kahan, Daniel; Mukai, Ryan; Ilott, Peter; Schratz, Brian; Soriano, Melissa; Finley, Susan; Shidner, Jeremy
During the Entry, Descent, and Landing (EDL) of NASA's Mars Science Laboratory (MSL), or Curiosity, rover to Gale Crater on Mars on August 6, 2012 UTC, the rover transmitted an X-band signal composed of carrier and tone frequencies and a UHF signal modulated with an 8kbps data stream. During EDL, the spacecraft's orientation is determined by its guidance and mechanical subsystems to ensure that the vehicle land safely at its destination. Although orientation to maximize telecom performance is not possible, antennas are especially designed and mounted to provide the best possible line of sight to Earth and to the Mars orbiters supporting MSL's landing. The tones and data transmitted over these links are selected carefully to reflect the most essential parameters of the vehicle's state and the performance of the EDL subsystems for post-EDL reconstruction should no further data transmission from the vehicle be possible. This paper addresses the configuration of the X band receive system used at NASA / JPL's Deep Space Network (DSN) to capture the signal spectrum of MSL's X band carrier and tone signal, examines the MSL vehicle state information obtained from the X band carrier signal only and contrasts the Doppler-derived information against the post-EDL known vehicle state. The paper begins with a description of the MSL EDL sequence of events and discusses the impact of the EDL maneuvers such as guided entry, parachute deploy, and powered descent on the frequency observables expected at the DSN. The range of Doppler dynamics possible is derived from extensive 6 Degrees-Of-Freedom (6 DOF) vehicle state calculations performed by MSL's EDL simulation team. The configuration of the DSN's receive system, using the Radio Science Receivers (RSR) to perform open-loop recording for both for nominal and off-nominal EDL scenarios, is detailed. Expected signal carrier power-to-noise levels during EDL are shown and their impact on signal detection is considered. Particula
Sleuthing the MSL EDL Performance from an X Band Carrier Perspective
NASA Technical Reports Server (NTRS)
Oudrhiri, Kamal; Asmar, Sami; Estabrook, Polly; Kahan, Daniel; Mukai, Ryan; Ilott, Peter; Schratz, Brian; Soriano, Melissa; Finley, Susan; Shidner, Jeremy
2013-01-01
During the Entry, Descent, and Landing (EDL) of NASA's Mars Science Laboratory (MSL), or Curiosity, rover to Gale Crater on Mars on August 6, 2012 UTC, the rover transmitted an X-band signal composed of carrier and tone frequencies and a UHF signal modulated with an 8kbps data stream. During EDL, the spacecraft's orientation is determined by its guidance and mechanical subsystems to ensure that the vehicle land safely at its destination. Although orientation to maximize telecom performance is not possible, antennas are especially designed and mounted to provide the best possible line of sight to Earth and to the Mars orbiters supporting MSL's landing. The tones and data transmitted over these links are selected carefully to reflect the most essential parameters of the vehicle's state and the performance of the EDL subsystems for post-EDL reconstruction should no further data transmission from the vehicle be possible. This paper addresses the configuration of the X band receive system used at NASA / JPL's Deep Space Network (DSN) to capture the signal spectrum of MSL's X band carrier and tone signal, examines the MSL vehicle state information obtained from the X band carrier signal only and contrasts the Doppler-derived information against the post-EDL known vehicle state. The paper begins with a description of the MSL EDL sequence of events and discusses the impact of the EDL maneuvers such as guided entry, parachute deploy, and powered descent on the frequency observables expected at the DSN. The range of Doppler dynamics possible is derived from extensive 6 Degrees-Of-Freedom (6 DOF) vehicle state calculations performed by MSL's EDL simulation team. The configuration of the DSN's receive system, using the Radio Science Receivers (RSR) to perform open-loop recording for both for nominal and off-nominal EDL scenarios, is detailed. Expected signal carrier power-to-noise levels during EDL are shown and their impact on signal detection is considered. Particular
NASA Astrophysics Data System (ADS)
Wang, Guowu; Li, Xiling; Wang, Peng; Zhang, Junming; Wang, Dian; Qiao, Liang; Wang, Tao; Li, Fashen
2018-06-01
The complex permeability and permittivity of the easy-plane anisotropic Co/polyimide composite at high temperature (293-673 K) in X band were measured. The results show that both the complex permeability and permittivity increase with the increase of temperature in the measured temperature range. The calculated absorption properties display that the intensity of the reflection loss (RL) peak first increases and then decreases with the increase of temperature, and reaches the maximum (-52 dB) at 523 K. At each temperature, the composite can achieve the RL exceeding -10 dB in the whole X band. The composite can even work stably for more than 20 min with the excellent absorption performance under 673 K. In addition, the RL performance of the composite at high temperature is better than that at room temperature.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Lee, Kiwoo; Natsui, Takuya; Hirai, Shunsuke
2011-06-01
One of the advantages of applying X-band linear accelerator (Linac) is the compact size of the whole system. That shows us the possibility of on-site system such as the custom inspection system in an airport. As X-ray source, we have developed X-band Linac and achieved maximum X-ray energy 950 keV using the low power magnetron (250 kW) in 2 {mu}s pulse length. The whole size of the Linac system is 1x1x1 m{sup 3}. That is realized by introducing X-band system. In addition, we have designed two-fold scintillator detector in dual energy X-ray concept. Monte carlo N-particle transport (MCNP) code wasmore » used to make up sensor part of the design with two scintillators, CsI and CdWO4. The custom inspection system is composed of two equipments: 950 keV X-band Linac and two-fold scintillator and they are operated simulating real situation such as baggage check in an airport. We will show you the results of experiment which was performed with metal samples: iron and lead as targets in several conditions.« less
Measurement of the Band-to-Band Registration of the SNPP VIIRS Imaging System from On-Orbit Data
NASA Technical Reports Server (NTRS)
Tilton, James C.; Lin, Guoqing; Tan, Bin
2016-01-01
The Visible Infrared Imaging Radiometer Suite (VIIRS) instrument was launched 28 October 2011 onboard the Suomi National Polar-orbiting Partnership (SNPP) satellite. The VIIRS instrument is a whiskbroom system with 22 spectral and thermal bands split between 16 moderate resolution bands (M-bands), five imagery resolution bands (I-bands) and a day-night band. In this study we measure the along-scan and along-track band-to-band registration between the I-bands and M-bands from on-orbit data. This measurement is performed by computing the Normalized Mutual Information (NMI) between shifted image band pairs and finding the amount of shift required (if any) to produce the peak in NMI value. Subpixel accuracy is obtained by utilizing bicubic interpolation. Registration shifts are found to be similar to pre-launch measurements and stable (within measurement error) over the instruments first four years in orbit.
NASA Astrophysics Data System (ADS)
Maneewong, Apichate; Seong, Baek Seok; Shin, Eun Joo; Kim, Jeong Seog; Kajornrith, Varavuth
2016-01-01
The color of pink tourmaline gemstone changed to colorless when heating at temperature of 600 °C in air. This colorless tourmaline recovered its pink color when irradiated with an electron beam (e-beam) of 800 kGy. The origin of the color change was investigated in three types of tourmaline gemstones, two pink are from Afghanistan and one green are from Nigeria, by using Ultraviolet-visible spectroscopy (UV-Vis), Fourier-transform infrared spectroscopy (FTIR), Electron paramagnetic resonance (EPR), and Energy Dispersive X-ray Fluorescence (EDXRF). The UV-Vis absorption spectrum of the pink tourmaline with higher Mn concentration (T2, 0.24 wt%) showed characteristic absorption peaks originating from the Mn3+ color center: two absorption bands centered at wavelength of 396 and 520 nm, respectively. Both absorption bands disappeared when heated in air at 600 °C and then reappeared when irradiated with an e-beam at 800 kGy. EPR T2 spectra showed that the color change was related to the valence change of Mn3+ to Mn2+ and vice versa. The pink tourmaline of lower MnO content (T1, 0.08 wt%) also became colorless when heated, but the color was not recovered when the gemstone underwent e-beam irradiation. Instead, a yellow color was obtained. UV-Vis and FTIR spectra indicated that this yellow color originated from a decomposition of the hydroxyl group (-OH) into O- and Ho by the e-beam irradiation. Green tourmaline did not show any color change with either heat treatment or e-beam irradiation.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Dolgonos, Alex; Mason, Thomas O.; Poeppelmeier, Kenneth R., E-mail: krp@northwestern.edu
2016-08-15
The direct optical band gap of semiconductors is traditionally measured by extrapolating the linear region of the square of the absorption curve to the x-axis, and a variation of this method, developed by Tauc, has also been widely used. The application of the Tauc method to crystalline materials is rooted in misconception–and traditional linear extrapolation methods are inappropriate for use on degenerate semiconductors, where the occupation of conduction band energy states cannot be ignored. A new method is proposed for extracting a direct optical band gap from absorption spectra of degenerately-doped bulk semiconductors. This method was applied to pseudo-absorption spectramore » of Sn-doped In{sub 2}O{sub 3} (ITO)—converted from diffuse-reflectance measurements on bulk specimens. The results of this analysis were corroborated by room-temperature photoluminescence excitation measurements, which yielded values of optical band gap and Burstein–Moss shift that are consistent with previous studies on In{sub 2}O{sub 3} single crystals and thin films. - Highlights: • The Tauc method of band gap measurement is re-evaluated for crystalline materials. • Graphical method proposed for extracting optical band gaps from absorption spectra. • The proposed method incorporates an energy broadening term for energy transitions. • Values for ITO were self-consistent between two different measurement methods.« less
DOE Office of Scientific and Technical Information (OSTI.GOV)
Heo, Sung; College of Information and Communication Engineering, Sungkyunkwan University, Cheoncheon-dong 300, Jangan-gu, Suwon 440-746; Lee, Hyung-Ik
2015-06-29
To investigate the band gap profile of Cu(In{sub 1−x},Ga{sub x})(Se{sub 1−y}S{sub y}){sub 2} of various compositions, we measured the band gap profile directly as a function of in-depth using high-resolution reflection energy loss spectroscopy (HR-REELS), which was compared with the band gap profile calculated based on the auger depth profile. The band gap profile is a double-graded band gap as a function of in-depth. The calculated band gap obtained from the auger depth profile seems to be larger than that by HR-REELS. Calculated band gaps are to measure the average band gap of the spatially different varying compositions with respectmore » to considering its void fraction. But, the results obtained using HR-REELS are to be affected by the low band gap (i.e., out of void) rather than large one (i.e., near void). Our findings suggest an analytical method to directly determine the band gap profile as function of in-depth.« less
NASA Astrophysics Data System (ADS)
Ludeno, Giovanni; Natale, Antonio; Soldovieri, Francesco; Vicinanza, Diego; Serafino, Francesco
2014-05-01
.2, pp. 231-235, April 2010. [2] Senet, C. M., Seemann, J., Flampouris, S., and Ziemer, F. (2008). Determination of bathymetric and current maps by the method DiSC based on the analysis of nautical X-Band radar image sequences of the sea surface (November 2007). IEEE Trans. on Geoscience and Remote Sensing, 46(8), 2267-2279. [3] F. Ziemer, and W. Rosenthal, "Directional spectra from shipboard navigation radar during LEWEX". Directional Ocean Wave Spectra: Measuring, Modeling, Predicting, and Applying, 1991 R. C. Beal, Ed., The Johns Hopkins University Press, pp. 125-127. [4] Weimin Huang ; Gill, E.," Surface Current Measurement Under Low Sea State Using Dual Polarized X-Band Nautical Radar", Selected Topics in Applied Earth Observations and Remote Sensing, IEEE Journal of, vol. 5, no.6, page 186-1873, 2012.
Use of EPR to Solve Biochemical Problems
Sahu, Indra D.; McCarrick, Robert M.; Lorigan, Gary A.
2013-01-01
EPR spectroscopy is a very powerful biophysical tool that can provide valuable structural and dynamic information on a wide variety of biological systems. The intent of this review is to provide a general overview for biochemists and biological researchers on the most commonly used EPR methods and how these techniques can be used to answer important biological questions. The topics discussed could easily fill one or more textbooks; thus, we present a brief background on several important biological EPR techniques and an overview of several interesting studies that have successfully used EPR to solve pertinent biological problems. The review consists of the following sections: an introduction to EPR techniques, spin labeling methods, and studies of naturally occurring organic radicals and EPR active transition metal systems which are presented as a series of case studies in which EPR spectroscopy has been used to greatly further our understanding of several important biological systems. PMID:23961941
Concentration by centrifugation for gas exchange EPR oximetry measurements with loop-gap resonators.
Subczynski, Witold K; Felix, Christopher C; Klug, Candice S; Hyde, James S
2005-10-01
Measurement of the bimolecular collision rate between a spin label and oxygen is conveniently carried out using a gas permeable plastic sample tube of small diameter that fits a loop-gap resonator. It is often desirable to concentrate the sample by centrifugation in order to improve the signal-to-noise ratio (SNR), but the deformable nature of small plastic sample tubes presents technical problems. Solutions to these problems are described. Two geometries were considered: (i) a methylpentene polymer, TPX, from Mitsui Chemicals, at X-band and (ii) Teflon tubing with 0.075 mm wall thickness at Q-band. Sample holders were fabricated from Delrin that fit the Eppendorf microcentrifuge tubes and support the sample capillaries. For TPX, pressure of the sealant at the end of the sample tube against the Delrin sample holder provided an adequate seal. For Teflon, the holder permitted introduction of water around the tube in order to equalize pressures across the sealant during centrifugation. Typically, the SNR was improved by a factor of five to eight. Oxygen accessibility applications in site-directed spin labeling studies are discussed.
Concentration by centrifugation for gas exchange EPR oximetry measurements with loop-gap resonators
NASA Astrophysics Data System (ADS)
Subczynski, Witold K.; Felix, Christopher C.; Klug, Candice S.; Hyde, James S.
2005-10-01
Measurement of the bimolecular collision rate between a spin label and oxygen is conveniently carried out using a gas permeable plastic sample tube of small diameter that fits a loop-gap resonator. It is often desirable to concentrate the sample by centrifugation in order to improve the signal-to-noise ratio (SNR), but the deformable nature of small plastic sample tubes presents technical problems. Solutions to these problems are described. Two geometries were considered: (i) a methylpentene polymer, TPX, from Mitsui Chemicals, at X-band and (ii) Teflon tubing with 0.075 mm wall thickness at Q-band. Sample holders were fabricated from Delrin that fit the Eppendorf microcentrifuge tubes and support the sample capillaries. For TPX, pressure of the sealant at the end of the sample tube against the Delrin sample holder provided an adequate seal. For Teflon, the holder permitted introduction of water around the tube in order to equalize pressures across the sealant during centrifugation. Typically, the SNR was improved by a factor of five to eight. Oxygen accessibility applications in site-directed spin labeling studies are discussed.
EPR investigation of UV light effect on calcium carbonate powders with different grain sizes.
Kabacińska, Zuzanna; Krzyminiewski, Ryszard; Dobosz, Bernadeta
2014-06-01
This study is based on investigation of calcium carbonate powders with different grain sizes exposed to UV light. Calcium carbonate is widely used in many branches of industry, e.g. as a filler for polymer materials; therefore, knowing its properties, among them also its reaction to UV light, is essential. Samples of powdered calcium carbonate with average grain sizes of 69 and 300 nm and 2.1, 6, 16, 25 µm were used in this investigation. Measurements were performed at room temperature using EPR X-band spectrometer, and they have shown the additional signals induced by the light from Hg lamp. The effect of annealing of the micro-grain samples was also studied. The spectra of four micro-grain samples after irradiation are similar, but there are differences between them and the other two powders, which could be related to the different sizes of their grains. Further studies based on these preliminary results may prove useful in research of photodegradation of CaCO3-filled materials, as well as helpful in increasing the accuracy of dating of archaeological and geological objects. © The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Yi, Hong; Liao, Zhixiong; Zhang, Guanghui
Abstract: The CuI/CuII and CuI/CuIII catalytic cycles have been subject to intense debate in the field of copper-catalyzed oxidative coupling reactions. A mechanistic study on the CuI/CuII redox process, by X-ray absorption (XAS) and electron paramagnetic resonance (EPR) spectroscopies, has elucidated the reduction mechanism of CuII to CuI by 1,3-diketone and detailed investigation revealed that the halide ion is important for the reduction process. The oxidative nature of the thereby-formed CuI has also been studied by XAS and EPR spectroscopy. This mechanistic information is applicable to the copper-catalyzed oxidative cyclization of b-ketocarbonyl derivatives to dihydrofurans. This protocol provides an idealmore » route to highly substituted dihydrofuran rings from easily available 1,3-dicarbonyls and olefins. Copper« less
Kittell, Aaron W.; Camenisch, Theodore G.; Ratke, Joseph J.; Sidabras, Jason W.; Hyde, James S.
2011-01-01
A continuous wave (CW) electron paramagnetic resonance (EPR) spectrum is typically displayed as the first harmonic response to the application of 100 kHz magnetic field modulation, which is used to enhance sensitivity by reducing the level of 1/f noise. However, magnetic field modulation of any amplitude causes spectral broadening and sacrifices EPR spectral intensity by at least a factor of two. In the work presented here, a CW rapid-scan spectroscopic technique that avoids these compromises and also provides a means of avoiding 1/f noise is developed. This technique, termed non-adiabatic rapid sweep (NARS) EPR, consists of repetitively sweeping the polarizing magnetic field in a linear manner over a spectral fragment with a small coil at a repetition rate that is sufficiently high that receiver noise, microwave phase noise, and environmental microphonics, each of which has 1/f characteristics, are overcome. Nevertheless, the rate of sweep is sufficiently slow that adiabatic responses are avoided and the spin system is always close to thermal equilibrium. The repetitively acquired spectra from the spectral fragment are averaged. Under these conditions, undistorted pure absorption spectra are obtained without broadening or loss of signal intensity. A digital filter such as a moving average is applied to remove high frequency noise, which is approximately equivalent in bandwidth to use of an integrating time constant in conventional field modulation with lock-in detection. Nitroxide spectra at L- and X-band are presented. PMID:21741868
The application of airborne imaging radars (L and X-band) to earth resources problems
NASA Technical Reports Server (NTRS)
Drake, B.; Shuchman, R. A.; Bryan, M. L.; Larson, R. W.; Liskow, C. L.; Rendleman, R. A.
1974-01-01
A multiplexed synthetic aperture Side-Looking Airborne Radar (SLAR) that simultaneously images the terrain with X-band (3.2 cm) and L-band (23.0 cm) radar wavelengths was developed. The Feasibility of using multiplexed SLAR to obtain useful information for earth resources purposes. The SLAR imagery, aerial photographs, and infrared imagery are examined to determine the qualitative tone and texture of many rural land-use features imaged. The results show that: (1) Neither X- nor L-band SLAR at moderate and low depression angles can directly or indirectly detect pools of water under standing vegetation. (2) Many of the urban and rural land-use categories present in the test areas can be identified and mapped on the multiplexed SLAR imagery. (3) Water resources management can be done using multiplexed SLAR. (4) Drainage patterns can be determined on both the X- and L-band imagery.
X-Band Radar for Studies of Tropical Storms from High Altitude UAV Platform
NASA Technical Reports Server (NTRS)
Rodriquez, Shannon; Heymsfield, Gerald; Li, Lihua; Bradley, Damon
2007-01-01
The increased role of unmanned aerial vehicles (UAV) in NASA's suborbital program has created a strong interest in the development of instruments with new capabilities, more compact sizes and reduced weights than the instruments currently operated on manned aircrafts. There is a strong demand and tremendous potential for using high altitude UAV (HUAV) to carry weather radars for measurements of reflectivity and wind fields from tropical storms. Tropical storm genesis frequently occurs in ocean regions that are inaccessible to piloted aircraft due to the long off shore range and the required periods of time to gather significant data. Important factors of interest for the study of hurricane genesis include surface winds, profiled winds, sea surface temperatures, precipitation, and boundary layer conditions. Current satellite precipitation and surface wind sensors have resolutions that are too large and revisit times that are too infrequent to study this problem. Furthermore, none of the spaceborne sensors measure winds within the storm itself. A dual beam X-band Doppler radar, UAV Radar (URAD), is under development at the NASA Goddard Space Flight Center for the study of tropical storms from HUAV platforms, such as a Global Hawk. X-band is the most desirable frequency for airborne weather radars since these can be built in a relatively compact size using off-the-shelf components which cost significantly less than other higher frequency radars. Furthermore, X-band radars provide good sensitivity with tolerable attenuation in storms. The low-cost and light-weight URAD will provide new capabilities for studying hurricane genesis by analyzing the vertical structure of tropical cyclones as well as 3D reflectivity and wind fields in clouds. It will enable us to measure both the 3D precipitation structure and surface winds by using two antenna beams: fixed nadir and conical scanning each produced by its associated subsystem. The nadir subsystem is a magnetron based radar
Direct Band Gap Gallium Antimony Phosphide (GaSbxP1−x) Alloys
Russell, H. B.; Andriotis, A. N.; Menon, M.; Jasinski, J. B.; Martinez-Garcia, A.; Sunkara, M. K.
2016-01-01
Here, we report direct band gap transition for Gallium Phosphide (GaP) when alloyed with just 1–2 at% antimony (Sb) utilizing both density functional theory based computations and experiments. First principles density functional theory calculations of GaSbxP1−x alloys in a 216 atom supercell configuration indicate that an indirect to direct band gap transition occurs at x = 0.0092 or higher Sb incorporation into GaSbxP1−x. Furthermore, these calculations indicate band edge straddling of the hydrogen evolution and oxygen evolution reactions for compositions ranging from x = 0.0092 Sb up to at least x = 0.065 Sb making it a candidate for use in a Schottky type photoelectrochemical water splitting device. GaSbxP1−x nanowires were synthesized by reactive transport utilizing a microwave plasma discharge with average compositions ranging from x = 0.06 to x = 0.12 Sb and direct band gaps between 2.21 eV and 1.33 eV. Photoelectrochemical experiments show that the material is photoactive with p-type conductivity. This study brings attention to a relatively uninvestigated, tunable band gap semiconductor system with tremendous potential in many fields. PMID:26860470
Energy dependence of the band-limited noise in black hole X-ray binaries★
NASA Astrophysics Data System (ADS)
Stiele, H.; Yu, W.
2015-10-01
Black hole low-mass X-ray binaries show a variety of variability features, which manifest as narrow peak-like structures superposed on broad noise components in power density spectra in the hard X-ray emission. In this work, we study variability properties of the band-limited noise component during the low-hard state for a sample of black hole X-ray binaries. We investigate the characteristic frequency and amplitude of the band-limited noise component and study covariance spectra. For observations that show a noise component with a characteristic frequency above 1 Hz in the hard energy band (4-8 keV), we found this very same component at a lower frequency in the soft band (1-2 keV). This difference in characteristic frequency is an indication that while both the soft and the hard band photons contribute to the same band-limited noise component, which likely represents the modulation of the mass accretion rate, the origin of the soft photons is actually further away from the black hole than the hard photons. Thus, the soft photons are characterized by larger radii, lower frequencies and softer energies, and are probably associated with a smaller optical depth for Comptonization up-scattering from the outer layer of the corona, or suggest a temperature gradient of the corona. We interpret this energy dependence within the picture of energy-dependent power density states as a hint that the contribution of the up-scattered photons originating in the outskirts of the Comptonizing corona to the overall emission in the soft band is becoming significant.
Johansson, M B; Kristiansen, P T; Duda, L; Niklasson, G A; Österlund, L
2016-11-30
Nanocrystalline tungsten trioxide (WO3) thin films prepared by DC magnetron sputtering have been studied using soft x-ray spectroscopy and optical spectrophotometry. Resonant inelastic x-ray scattering (RIXS) measurements reveal band gap states in sub-stoichiometric γ-WO3-x with x = 0.001-0.005. The energy positions of these states are in good agreement with recently reported density functional calculations. The results were compared with optical absorption measurements in the near infrared spectral region. An optical absorption peak at 0.74 eV is assigned to intervalence transfer of polarons between W sites. A less prominent peak at energies between 0.96 and 1.16 eV is assigned to electron excitation of oxygen vacancies. The latter results are supported by RIXS measurements, where an energy loss in this energy range was observed, and this suggests that electron transfer processes involving transitions from oxygen vacancy states can be observed in RIXS. Our results have implications for the interpretation of optical properties of WO3, and the optical transitions close to the band gap, which are important in photocatalytic and photoelectrochemical applications.
EPR study of copper(II) ions in zinc 1-malate trihydrate
NASA Astrophysics Data System (ADS)
Bonomo, Raffaele P.; Di Bilio, Angel J.; Riggi, Francesco
1988-10-01
The EPR spectrum of Cu 2+ ions in zinc 1-malate trihydrate has been measured at 150 K for a large number of orientations of the applied magnetic field. Analysis yields the following spin Hamiltonian parameters: g x=2.0894±0.0009, A x=-12.0±1.5, g y=2.0879±0.0005, A y=-8.7±1.0, R=-0.7±1.5, g z=2.4249±0.0005, A z=-120.1±0.9, P=9.9±0.5, where the units of A and P are 10 4 cm -1. The Zeeman and hyperfine coupling tensors are coincident within 2°. The spectrum shows forbidden transitions with abnormal intensity due to a large quadrupolar interaction. The direction of g z points towards the hydroxyl oxygen while the g x and g y directions lie approximately along the metal-carboxylate oxygen bond.
EPR Investigation of Gamma-Irradiated Rapana Thomasiana (Gastropoda, Muricidae) Shell
DOE Office of Scientific and Technical Information (OSTI.GOV)
Seletchi, Emilia Dana; Duliu, Octavian G.; Georgescu, Rodica
2007-04-23
The shell of Rapana Thomasiana snail, a carnivorous gastropod collected from the coasts of the Black Sea (Romania) was investigated by using Electron Paramagnetic Resonance (EPR) spectroscopy. The samples in powder form were irradiated with a 60Co gamma-ray source at ambient temperature in the dose range between 1.06 and 11.3 kGy. The measurements showed that the EPR signal intensity enhanced following saturation exponential with the absorbed dose. The estimated EPR parameters: g1 = 1.9976, g2 = 2.0006, g3 = 2.0015, g4 = 2.0030 and g5 = 2.0043 revealed a complex spectrum consisting of CO{sub 2}{sup -}, CO{sub 3}{sup 3-} andmore » CO{sub 3}{sup -} species. A very weak signal at g6 = 2.0057 was associated to SO{sub 2}{sup -} electron center. All EPR signals of gamma-irradiated samples decreased with various rate with the of 100 deg. C isothermal annealing time.« less
Computer-Automated Evolution of Spacecraft X-Band Antennas
NASA Technical Reports Server (NTRS)
Lohn, Jason D.; Homby, Gregory S.; Linden, Derek S.
2010-01-01
A document discusses the use of computer- aided evolution in arriving at a design for X-band communication antennas for NASA s three Space Technology 5 (ST5) satellites, which were launched on March 22, 2006. Two evolutionary algorithms, incorporating different representations of the antenna design and different fitness functions, were used to automatically design and optimize an X-band antenna design. A set of antenna designs satisfying initial ST5 mission requirements was evolved by use these algorithms. The two best antennas - one from each evolutionary algorithm - were built. During flight-qualification testing of these antennas, the mission requirements were changed. After minimal changes in the evolutionary algorithms - mostly in the fitness functions - new antenna designs satisfying the changed mission requirements were evolved and within one month of this change, two new antennas were designed and prototypes of the antennas were built and tested. One of these newly evolved antennas was approved for deployment on the ST5 mission, and flight-qualified versions of this design were built and installed on the spacecraft. At the time of writing the document, these antennas were the first computer-evolved hardware in outer space.
Determining Tidal Phase Differences from X-Band Radar Images
NASA Astrophysics Data System (ADS)
Newman, Kieran; Bell, Paul; Brown, Jennifer; Plater, Andrew
2017-04-01
Introduction Previous work by Bell et. al. (2016) has developed a method using X-band marine radar to measure intertidal bathymetry, using the waterline as a level over a spring-neap tidal cycle. This has been used in the Dee Estuary to give a good representation of the bathymetry in the area. However, there are some sources of inaccuracy in the method, as a uniform spatial tidal signal is assumed over the entire domain. Motivation The method used by Bell et. al. (2016) applies a spatially uniform tidal signal to the entire domain. This fails to account for fine-scale variations in water level and tidal phase. While methods are being developed to account for small-scale water level variations using high resolution modelling, a method to determine tidal phase variations directly from the radar intensity images could be advantageous operationally. Methods The tidal phase has been computed using two different methods, with hourly averaged images from 2008. In the first method, the cross-correlation between each raw pixel time series and a tidal signal at a number of lags is calculated, and the lag with the highest correlation to the pixel series is recorded. For the second method, the same method of correlation is used on signals generated by tracking movement of buoys, which show up strongly in the radar image as they move on their moorings with the tidal currents. There is a broad agreement between the two methods, but validation is needed to determine the relative accuracy. The phase has also been calculated using a Fourier decomposition, and agrees broadly with the above methods. Work also needs to be done to separate areas where the recorded phase is due to tidal current (mostly subtidal areas) or due to elevation (mostly the wetting/drying signal in intertidal areas), by classifying radar intensities by the phases and amplitudes of the tides. Filtering out signal variations due to wind strength and attenuation of the radar signal will also be applied. Validation
X-ray source development for EXAFS measurements on the National Ignition Facility.
Coppari, F; Thorn, D B; Kemp, G E; Craxton, R S; Garcia, E M; Ping, Y; Eggert, J H; Schneider, M B
2017-08-01
Extended X-ray absorption Fine Structure (EXAFS) measurements require a bright, spectrally smooth, and broad-band x-ray source. In a laser facility, such an x-ray source can be generated by a laser-driven capsule implosion. In order to optimize the x-ray emission, different capsule types and laser irradiations have been tested at the National Ignition Facility (NIF). A crystal spectrometer is used to disperse the x-rays and high efficiency image plate detectors are used to measure the absorption spectra in transmission geometry. EXAFS measurements at the K-edge of iron at ambient conditions have been obtained for the first time on the NIF laser, and the requirements for optimization have been established.
Energy distribution measurement of narrow-band ultrashort x-ray beams via K-edge filters subtraction
DOE Office of Scientific and Technical Information (OSTI.GOV)
Cardarelli, Paolo; Di Domenico, Giovanni; Marziani, Michele
2012-10-01
The characterization of novel x-ray sources includes the measurement of the photon flux and the energy distribution of the produced beam. The aim of BEATS2 experiment at the SPARC-LAB facility of the INFN National Laboratories of Frascati (Rome, Italy) is to investigate possible medical applications of an x-ray source based on Thomson relativistic back-scattering. This source is expected to produce a pulsed quasi-monochromatic x-ray beam with an instantaneous flux of 10{sup 20} ph/s in pulses 10 ps long and with an average energy of about 20 keV. A direct measurement of energy distribution of this beam is very difficult withmore » traditional detectors because of the extremely high photon flux. In this paper, we present a method for the evaluation of the energy distribution of quasi-monochromatic x-ray beams based on beam filtration with K-edge absorbing foils in the energy range of interest (16-22 keV). The technique was tested measuring the energy distribution of an x-ray beam having a spectrum similar to the expected one (SPARC-LAB Thomson source) by using a tungsten anode x-ray tube properly filtered and powered. The energy distribution obtained has been compared with the one measured with a HPGe detector showing very good agreement.« less
DOE Office of Scientific and Technical Information (OSTI.GOV)
Webster, P. T.; Riordan, N. A.; Liu, S.
2015-12-28
The structural and optical properties of lattice-matched InAs{sub 0.911}Sb{sub 0.089} bulk layers and strain-balanced InAs/InAs{sub 1−x}Sb{sub x} (x ∼ 0.1–0.4) superlattices grown on (100)-oriented GaSb substrates by molecular beam epitaxy are examined using X-ray diffraction, spectroscopic ellipsometry, and temperature dependent photoluminescence spectroscopy. The photoluminescence and ellipsometry measurements determine the ground state bandgap energy and the X-ray diffraction measurements determine the layer thickness and mole fraction of the structures studied. Detailed modeling of the X-ray diffraction data is employed to quantify unintentional incorporation of approximately 1% Sb into the InAs layers of the superlattices. A Kronig-Penney model of the superlattice miniband structure ismore » used to analyze the valence band offset between InAs and InAsSb, and hence the InAsSb band edge positions at each mole fraction. The resulting composition dependence of the bandgap energy and band edge positions of InAsSb are described using the bandgap bowing model; the respective low and room temperature bowing parameters for bulk InAsSb are 938 and 750 meV for the bandgap, 558 and 383 meV for the conduction band, and −380 and −367 meV for the valence band.« less
Use of multi-coil parallel-gap resonators for co-registration EPR/NMR imaging
NASA Astrophysics Data System (ADS)
Kawada, Yuuki; Hirata, Hiroshi; Fujii, Hirodata
2007-01-01
This article reports experimental investigations on the use of RF resonators for continuous-wave electron paramagnetic resonance (cw-EPR) and proton nuclear magnetic resonance (NMR) imaging. We developed a composite resonator system with multi-coil parallel-gap resonators for co-registration EPR/NMR imaging. The resonance frequencies of each resonator were 21.8 MHz for NMR and 670 MHz for EPR. A smaller resonator (22 mm in diameter) for use in EPR was placed coaxially in a larger resonator (40 mm in diameter) for use in NMR. RF magnetic fields in the composite resonator system were visualized by measuring a homogeneous 4-hydroxy-2,2,6,6-tetramethyl-piperidinooxy (4-hydroxy-TEMPO) solution in a test tube. A phantom of five tubes containing distilled water and 4-hydroxy-TEMPO solution was also measured to demonstrate the potential usefulness of this composite resonator system in biomedical science. An image of unpaired electrons was obtained for 4-hydroxy-TEMPO in three tubes, and was successfully mapped on the proton image for five tubes. Technical problems in the implementation of a composite resonator system are discussed with regard to co-registration EPR/NMR imaging for animal experiments.
Mini-RF S- and X-band Bistatic Observations of the Floor of Cabeus Crater
NASA Astrophysics Data System (ADS)
Patterson, Gerald Wesley; Stickle, Angela; Turner, Franklin; Jensen, James; Cahill, Joshua; Mini-RF Team
2017-10-01
The Mini-RF instrument aboard NASA’s Lunar Reconnaissance Orbiter (LRO) is a hybrid dual-polarized synthetic aperture radar (SAR) and operates in concert with the Arecibo Observatory (AO) and the Goldstone deep space communications complex 34 meter antenna DSS-13 to collect S- and X-band bistatic radar data of the Moon. Bistatic radar data provide a means to probe the near subsurface for the presence of water ice, which exhibits a strong response in the form of a Coherent Backscatter Opposition Effect (CBOE). This effect has been observed in radar data for the icy surfaces of the Galilean satellites, the polar caps of Mars, polar craters on Mercury, and terrestrial ice sheets in Greenland. Previous work using Mini-RF S-band (12.6 cm) bistatic data suggests the presence of a CBOE associated with the floor of the lunar south polar crater Cabeus. The LRO spacecraft has begun its third extended mission. For this phase of operations Mini-RF is leveraging the existing AO architecture to make S-band radar observations of additional polar craters (e.g., Haworth, Shoemaker, Faustini). The purpose of acquiring these data is to determine whether other polar craters exhibit the response observed for Cabeus. Mini-RF has also initiated a new mode of operation that utilizes the X-band (4.2cm) capability of the instrument receiver and a recently commissioned X/C-band transmitter within the Deep Space Network’s (DSN) Goldstone complex to collect bistatic X-band data of the Moon. The purpose of acquiring these data is to constrain the depth/thickness of materials that exhibit a CBOE response - with an emphasis on observing the floor of Cabeus. Recent Mini-RF X-band observations of the floors of the craters Cabeus do not show evidence for a CBOE. This would suggest that the upper ~0.5 meters of the regolith for the floor of Cabeus do not harber water ice in a form detectable at 4.2 cm wavelengths.
Callens, F; Vanhaelewyn, G; Matthys, P
2002-04-01
Electron Paramagnetic Resonance (EPR) applications like e.g. EPR dosimetry and dating, are usually performed at X-band frequencies because of practical reasons (cost, sample size, etc.). However, it is increasingly recognized that the radiation-induced EPR signals are strongly composite, what might affect dose/age estimates. A few recent examples from both the dosimetry and dating field, illustrating the problems, will be presented. The involved spectra are mainly due to carbonate-derived radicals (CO2-, CO3(3-), etc.). Measurements at higher microwave frequencies are often recommended to improve the insight into the spectra and/or the practical signal quantification. Recent results at Q- and W-band frequencies will show that a multi-frequency approach indeed opens many interesting perspectives in this field but also that each frequency may have specific (dis)advantages depending on the EPR probe and application involved. The discussion will concern carbonate-containing apatite single crystals, shells, modern and fossil tooth enamel.
Toward broad-band x-ray detected ferromagnetic resonance in longitudinal geometry
DOE Office of Scientific and Technical Information (OSTI.GOV)
Ollefs, K.; European Synchrotron Radiation Facility; Meckenstock, R.
2015-06-14
An ultrahigh-vacuum-compatible setup for broad-band X-ray detected ferromagnetic resonance (XFMR) in longitudinal geometry is introduced which relies on a low-power, continuous-wave excitation of the ferromagnetic sample. A simultaneous detection of the conventional ferromagnetic resonance via measuring the reflected microwave power and the XFMR signal of the X-ray absorption is possible. First experiments on the Fe and Co L{sub 3}-edges of a permalloy film covered with Co nanostripes as well as the Fe and Ni K-edges of a permalloy film are presented and discussed. Two different XFMR signals are found, one of which is independent of the photon energy and thereforemore » does not provide element-selective information. The other much weaker signal is element-selective, and the dynamic magnetic properties could be detected for Fe and Co separately. The dependence of the latter XFMR signal on the photon helicity of the synchrotron light is found to be distinct from the usual x-ray magnetic circular dichroism effect.« less
Effect of Γ-X band mixing on the donor binding energy in a Quantum Wire
NASA Astrophysics Data System (ADS)
Vijaya Shanthi, R.; Jayakumar, K.; Nithiananthi, P.
2015-02-01
To invoke the technological applications of heterostructure semiconductors like Quantum Well (QW), Quantum Well Wire (QWW) and Quantum Dot (QD), it is important to understand the property of impurity energy which is responsible for the peculiar electronic & optical behavior of the Low Dimensional Semiconductor Systems (LDSS). Application of hydrostatic pressure P>35kbar drastically alters the band offsets leading to the crossover of Γ band of the well & X band of the barrier resulting in an indirect transition of the carrier and this effect has been studied experimentally and theoretically in a QW structure. In this paper, we have investigated the effect of Γ-X band mixing due to the application of hydrostatic pressure in a GaAs/AlxGa1-xAs QWW system. The results are presented and discussed for various widths of the wire.
Multi-photon transitions and Rabi resonance in continuous wave EPR.
Saiko, Alexander P; Fedaruk, Ryhor; Markevich, Siarhei A
2015-10-01
The study of microwave-radiofrequency multi-photon transitions in continuous wave (CW) EPR spectroscopy is extended to a Rabi resonance condition, when the radio frequency of the magnetic-field modulation matches the Rabi frequency of a spin system in the microwave field. Using the non-secular perturbation theory based on the Bogoliubov averaging method, the analytical description of the response of the spin system is derived for all modulation frequency harmonics. When the modulation frequency exceeds the EPR linewidth, multi-photon transitions result in sidebands in absorption EPR spectra measured with phase-sensitive detection at any harmonic. The saturation of different-order multi-photon transitions is shown to be significantly different and to be sensitive to the Rabi resonance. The noticeable frequency shifts of sidebands are found to be the signatures of this resonance. The inversion of two-photon lines in some spectral intervals of the out-of-phase first-harmonic signal is predicted under passage through the Rabi resonance. The inversion indicates the transition from absorption to stimulated emission or vice versa, depending on the sideband. The manifestation of the primary and secondary Rabi resonance is also demonstrated in the time evolution of steady-state EPR signals formed by all harmonics of the modulation frequency. Our results provide a theoretical framework for future developments in multi-photon CW EPR spectroscopy, which can be useful for samples with long spin relaxation times and extremely narrow EPR lines. Copyright © 2015 Elsevier Inc. All rights reserved.
Kavalenka, Aleh; Urbancic, Iztok; Belle, Valérie; Rouger, Sabrina; Costanzo, Stéphanie; Kure, Sandra; Fournel, André; Longhi, Sonia; Guigliarelli, Bruno; Strancar, Janez
2010-03-17
To characterize the structure of dynamic protein systems, such as partly disordered protein complexes, we propose a novel approach that relies on a combination of site-directed spin-labeled electron paramagnetic resonance spectroscopy and modeling of local rotation conformational spaces. We applied this approach to the intrinsically disordered C-terminal domain of the measles virus nucleoprotein (N(TAIL)) both free and in complex with the X domain (XD, aa 459-507) of the viral phosphoprotein. By comparing measured and modeled temperature-dependent restrictions of the side-chain conformational spaces of 12 SL cysteine-substituted N(TAIL) variants, we showed that the 490-500 region of N(TAIL) is prestructured in the absence of the partner, and were able to quantitatively estimate, for the first time to our knowledge, the extent of the alpha-helical sampling of the free form. In addition, we showed that the 505-525 region of N(TAIL) conserves a significant degree of freedom even in the bound form. The latter two findings provide a mechanistic explanation for the reported rather high affinity of the N(TAIL)-XD binding reaction. Due to the nanosecond timescale of X-band EPR spectroscopy, we were also able to monitor the disordering in the 488-525 region of N(TAIL), in particular the unfolding of the alpha-helical region when the temperature was increased from 281 K to 310 K. Copyright 2010 Biophysical Society. Published by Elsevier Inc. All rights reserved.
The modification of X and L band radar signals by monomolecular sea slicks
NASA Technical Reports Server (NTRS)
Huehnerfuss, H.; Alpers, W.; Cross, A.; Garrett, W. D.; Keller, W. C.; Plant, W. J.; Schuler, D. L.; Lange, P. A.; Schlude, F.
1983-01-01
One methyl oleate and two oleyl alcohol surface films were produced on the surface of the North Sea under comparable oceanographic and meteorological conditions in order to investigate their influence on X and L band radar backscatter. Signals are backscattered in these bands primarily by surface waves with lengths of about 2 and 12 cm, respectively, and backscattered power levels in both bands were reduced by the slicks. The reduction was larger at X band than at L band, however, indicating that shorter waves are more intensely damped by the surface films. The oleyl alcohol film caused greater attenuation of short gravity waves than the film of methyl oleate, thus demonstrating the importance of the physicochemical properties of films on the damping of wind-generated gravity capillary waves. Finally, these experiments indicate a distinct dependence of the degree of damping on the angle between wind and waves. Wind-generated waves traveling in the wind direction are more intensely damped by surface films than are waves traveling at large angles to the wind.
Olczyk, Paweł; Komosinska-Vassev, Katarzyna; Ramos, Paweł; Mencner, Łukasz; Olczyk, Krystyna; Pilawa, Barbara
2015-07-25
Electron paramagnetic resonance (EPR) spectroscopy was used to examine insulins interactions with free radicals. Human recombinant DNA insulins of three groups were studied: short-acting insulin (Insuman Rapid); intermediate-acting insulins (Humulin N, Insuman Basal), and pre-mixed insulins (Humulin M3, Gensulin M50, Gensulin M40, Gensulin M30). The aim of an X-band (9.3GHz) study was comparative analysis of antioxidative properties of the three groups of human insulins. DPPH was used as a stable free radical model. Amplitudes of EPR lines of DPPH as the paramagnetic free radical reference, and DPPH interacting with the individual tested insulins were compared. For all the examined insulins kinetics of their interactions with free radicals up to 60 min were obtained. The strongest interactions with free radicals were observed for the short-acting insulin - Insuman Rapid. The lowest interactions with free radicals were characteristic for intermediate-acting insulin - Insuman Basal. The pre-mixed insulins i.e. Humulin M3 and Gensulin M50 revealed the fastest interactions with free radicals. The short acting, intermediate acting and premixed insulins have been found to be effective agents in reducing free radical formation in vitro and should be further considered as potential useful tools in attenuation of oxidative stress in diabetic patients. Copyright © 2015 Elsevier B.V. All rights reserved.
Measuring the critical band for speech.
Healy, Eric W; Bacon, Sid P
2006-02-01
The current experiments were designed to measure the frequency resolution employed by listeners during the perception of everyday sentences. Speech bands having nearly vertical filter slopes and narrow bandwidths were sharply partitioned into various numbers of equal log- or ERBN-width subbands. The temporal envelope from each partition was used to amplitude modulate a corresponding band of low-noise noise, and the modulated carriers were combined and presented to normal-hearing listeners. Intelligibility increased and reached asymptote as the number of partitions increased. In the mid- and high-frequency regions of the speech spectrum, the partition bandwidth corresponding to asymptotic performance matched current estimates of psychophysical tuning across a number of conditions. These results indicate that, in these regions, the critical band for speech matches the critical band measured using traditional psychoacoustic methods and nonspeech stimuli. However, in the low-frequency region, partition bandwidths at asymptote were somewhat narrower than would be predicted based upon psychophysical tuning. It is concluded that, overall, current estimates of psychophysical tuning represent reasonably well the ability of listeners to extract spectral detail from running speech.
Radiation accident dosimetry on plastics by EPR spectrometry.
Trompier, F; Bassinet, C; Clairand, I
2010-02-01
In case of acute exposure to ionizing radiation, the dose absorbed by the victims has to be rapidly and accurately assessed in order to choose an appropriate medical treatment. Tooth enamel and bone biopsies measured by EPR spectrometry are often used as dose indicators, due to the good radiation sensitivity and the stability of EPR radiation-sensitive signals. Nevertheless, the invasive sampling of teeth and bones limits the application of this technique to retrospective dosimetry. Therefore, we have investigated an alternative non-invasive methodology. We have surveyed with EPR spectrometry the dosimetric properties of the plastics that can be found in personal effects such as glasses (CR-39, polycarbonate), mobile phones (PMMA, polycarbonate), watches and buttons. Dose response, signal stability and effects of storage conditions were investigated. Significant signal fading limits the use for radiation accident dosimetry. Few plastics present the required characteristics to be used in case of a radiation accident.
NASA Technical Reports Server (NTRS)
Stark, G.; Smith, P. L.; Ito, K.; Yoshino, K.
1992-01-01
Photodissociation following absorption of extreme-ultraviolet photons is an important factor in determining the abundance and isotropic fractionation of CO in diffuse and translucent interstellar clouds. The principal channel for destruction of CO-13 in such clouds begins with absorption in the (1,0) vibrational band of the E1Pi - X1Sigma(+) system; similarly, absorption in the (0,0) band begins a significant destruction channel for CO-12. Reliable modeling of the CO fractionation process depends critically upon the accuracy of the photoabsorption cross section for these bands. We have measured the cross sections for the relevant isotropic species and for the (1,0) band of CO-12. Our results, which are uncertain by about 10 percent, are for the most part larger than previous measurements.
Intensity measurements for the /2, O/ gamma-band of O2, b 1Sigma-g/+/ - X 3Sigma-g/-/
NASA Technical Reports Server (NTRS)
Miller, J. H.; Giver, L. P.; Boese, R. W.
1976-01-01
Line intensities for the P sub P and P sub Q branches of the (2-O) vibrational band of the magnetic dipole electronic transition for the oxygen red system at 6280 A were measured, and the sum of the R sub R and R sub Q branch intensities was taken. A large number of repetitive spectral scans were required for accuracy, because of low absorption values even at optical path lengths from 300 to 600 m. A total of 557 individual measurements of P-branch lines yielded an intensity value for the P-branches, and equivalent widths for 24 spectral scans yielded an intensity value for the R-branch. R-branch to P-branch intensity ratios were taken for the A-band, B-band, and gamma-band (respectively, O-O at 7620 A, 1-O at 6880 A, and 2-O at 6280 A). Intensities for some rotational lines are found, and effects of combined rotation-vibration interaction are probed.
NASA Technical Reports Server (NTRS)
VanKeuls, F. W.; Mueller, C. H.; Miranda, F. A.; Romanofsky, R. R.; Canedy, C. L.; Aggarwal, S.; Venkatesan, T.; Ramesh, R.; Horwitz, S.; Chang, W.
1999-01-01
We report on measurements taken on over twenty Ku-band coupled microstrip phase shifters (CMPS) using thin ferroelectric films of Ba(x)Sr(1-x)TiO3. This CMPS design is a recent innovation designed to take advantage of the high tunability and tolerate the high dielectric constant of ferroelectric films at Ku- and K-band frequencies. These devices are envisioned as a component in low-cost steerable beam phased area antennas, Comparisons are made between devices with differing film thickness, annealed vs unannealed, Mn-doped vs. undoped, and also substrates of LaAlO3 and MgO. A comparison between the CMPS structure and a CPW phase shifter was also made oil the same ferroelectric film.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Sutter-Fella, Carolin M.; Miller, D. Westley; Ngo, Quynh P.
Organometal halide perovskite semiconductors have emerged as promising candidates for optoelectronic applications because of the outstanding charge carrier transport properties, achieved with low-temperature synthesis. In this paper, we present highly sensitive sub-bandgap external quantum efficiency (EQE) measurements of Au/spiro-OMeTAD/CH 3NH 3Pb(I 1–xBr x) 3/TiO 2/FTO/glass photovoltaic devices. The room-temperature spectra show exponential band tails with a sharp onset characterized by low Urbach energies (E u) over the full halide composition space. The Urbach energies are 15–23 meV, lower than those for most semiconductors with similar bandgaps (especially with E g > 1.9 eV). Intentional aging of CH 3NH 3Pb(I 1–xBrmore » x) 3 for up to 2300 h, reveals no change in E u, despite the appearance of the PbI 2 phase due to decomposition, and confirms a high degree of crystal ordering. Moreover, sub-bandgap EQE measurements reveal an extended band of sub-bandgap electronic states that can be fit with one or two point defects for pure CH 3NH 3PbI 3 or mixed CH 3NH 3Pb(I 1–xBr x) 3 compositions, respectively. Finally, the study provides experimental evidence of defect states close to the midgap that could impact photocarrier recombination and energy conversion efficiency in higher bandgap CH 3NH 3Pb(I 1–xBr x) 3 alloys.« less
Sutter-Fella, Carolin M.; Miller, D. Westley; Ngo, Quynh P.; ...
2017-02-15
Organometal halide perovskite semiconductors have emerged as promising candidates for optoelectronic applications because of the outstanding charge carrier transport properties, achieved with low-temperature synthesis. In this paper, we present highly sensitive sub-bandgap external quantum efficiency (EQE) measurements of Au/spiro-OMeTAD/CH 3NH 3Pb(I 1–xBr x) 3/TiO 2/FTO/glass photovoltaic devices. The room-temperature spectra show exponential band tails with a sharp onset characterized by low Urbach energies (E u) over the full halide composition space. The Urbach energies are 15–23 meV, lower than those for most semiconductors with similar bandgaps (especially with E g > 1.9 eV). Intentional aging of CH 3NH 3Pb(I 1–xBrmore » x) 3 for up to 2300 h, reveals no change in E u, despite the appearance of the PbI 2 phase due to decomposition, and confirms a high degree of crystal ordering. Moreover, sub-bandgap EQE measurements reveal an extended band of sub-bandgap electronic states that can be fit with one or two point defects for pure CH 3NH 3PbI 3 or mixed CH 3NH 3Pb(I 1–xBr x) 3 compositions, respectively. Finally, the study provides experimental evidence of defect states close to the midgap that could impact photocarrier recombination and energy conversion efficiency in higher bandgap CH 3NH 3Pb(I 1–xBr x) 3 alloys.« less
MMIC linear-phase and digital modulators for deep space spacecraft X-band transponder applications
NASA Technical Reports Server (NTRS)
Mysoor, Narayan R.; Ali, Fazal
1991-01-01
The design concepts, analyses, and development of GaAs monolithic microwave integrated circuit (MMIC) linear-phase and digital modulators for the next generation of space-borne communications systems are summarized. The design approach uses a compact lumped element quadrature hybrid and Metal Semiconductor Field Effect Transistors (MESFET)-varactors to provide low loss and well-controlled phase performance for deep space transponder (DST) applications. The measured results of the MESFET-diode show a capacitance range of 2:1 under reverse bias, and a Q of 38 at 10 GHz. Three cascaded sections of hybrid-coupled reflection phase shifters were modeled and simulations performed to provide an X-band (8415 +/- 50 MHz) DST phase modulator with +/- 2.5 radians of peak phase deviation. The modulator will accommodate downlink signal modulation with composite telemetry and ranging data, with a deviation linearity tolerance of +/- 8 percent and insertion loss of less than 8 +/- 0.5 dB. The MMIC digital modulator is designed to provide greater than 10 Mb/s of bi-phase modulation at X-band.
Energy band gap and spectroscopic studies in Mn{sub 1-x}Cu{sub x}WO{sub 4} (0 ≤ x ≤ 0.125)
DOE Office of Scientific and Technical Information (OSTI.GOV)
Mal, Priyanath; Rambabu, P.; Turpu, G. R.
2016-05-06
A study on the effect of nonmagnetic Cu{sup 2+} substitution at Mn{sup 2+} site on the structural and energy band gap of the MnWO{sub 4} is reported. Convenient solid state reaction route has been adopted for the synthesis of Mn{sub 1-x}Cu{sub x}WO{sub 4}. X-ray diffraction (XRD) pattern showed high crystalline quality of the prepared samples. Raman spectroscopic studies were carried out to understand the structural aspects of the doping. 15 Raman active modes were identified out of 18, predicted for wolframite type monoclinic structure of MnWO{sub 4}. UV-visible diffuse reflectance spectra were recorded and analyzed to get energy band gapmore » of the studied system and are found in the range of 2.5 eV to 2.04 eV with a systematic decrease with the increase in Cu{sup 2+} concentration. Energy band gap values are verified by Density Functional Theory calculations based on projector augmented wave (PAW) method. The calculated values are in good agreement with the experimental data.« less
Calibration of helical tomotherapy machine using EPR/alanine dosimetry.
Perichon, Nicolas; Garcia, Tristan; François, Pascal; Lourenço, Valérie; Lesven, Caroline; Bordy, Jean-Marc
2011-03-01
Current codes of practice for clinical reference dosimetry of high-energy photon beams in conventional radiotherapy recommend using a 10 x 10 cm2 square field, with the detector at a reference depth of 10 cm in water and 100 cm source to surface distance (SSD) (AAPM TG-51) or 100 cm source-to-axis distance (SAD) (IAEA TRS-398). However, the maximum field size of a helical tomotherapy (HT) machine is 40 x 5 cm2 defined at 85 cm SAD. These nonstandard conditions prevent a direct implementation of these protocols. The purpose of this study is twofold: To check the absorbed dose in water and dose rate calibration of a tomotherapy unit as well as the accuracy of the tomotherapy treatment planning system (TPS) calculations for a specific test case. Both topics are based on the use of electron paramagnetic resonance (EPR) using alanine as transfer dosimeter between the Laboratoire National Henri Becquerel (LNHB) 60Co-gamma-ray reference beam and the Institut Curie's HT beam. Irradiations performed in the LNHB reference 60Co-gamma-ray beam allowed setting up the calibration method, which was then implemented and tested at the LNHB 6 MV linac x-ray beam, resulting in a deviation of 1.6% (at a 1% standard uncertainty) relative to the reference value determined with the standard IAEA TRS-398 protocol. HT beam dose rate estimation shows a difference of 2% with the value stated by the manufacturer at a 2% standard uncertainty. A 4% deviation between measured dose and the calculation from the tomotherapy TPS was found. The latter was originated by an inadequate representation of the phantom CT-scan values and, consequently, mass densities within the phantom. This difference has been explained by the mass density values given by the CT-scan and used by the TPS which were not the true ones. Once corrected using Monte Carlo N-Particle simulations to validate the accuracy of this process, the difference between corrected TPS calculations and alanine measured dose values was then
Uchiyama, Hidefumi; Zhao, Qing-Li; Hassan, Mariame Ali; Andocs, Gabor; Nojima, Nobuyuki; Takeda, Keigo; Ishikawa, Kenji; Hori, Masaru; Kondo, Takashi
2015-01-01
Electron paramagnetic resonance (EPR)-spin trapping and flow cytometry were used to identify free radicals generated using argon-cold atmospheric plasma (Ar-CAP) in aqueous solutions and intracellularly in comparison with those generated by X-irradiation. Ar-CAP was generated using a high-voltage power supply unit with low-frequency excitation. The characteristics of Ar-CAP were estimated by vacuum UV absorption and emission spectra measurements. Hydroxyl (·OH) radicals and hydrogen (H) atoms in aqueous solutions were identified with the spin traps 5,5-dimethyl-1-pyrroline N-oxide (DMPO), 3,3,5,5-tetramethyl-1-pyrroline-N-oxide (M4PO), and phenyl N-t-butylnitrone (PBN). The occurrence of Ar-CAP-induced pyrolysis was evaluated using the spin trap 3,5-dibromo-4-nitrosobenzene sulfonate (DBNBS) in aqueous solutions of DNA constituents, sodium acetate, and L-alanine. Human lymphoma U937 cells were used to study intracellular oxidative stress using five fluorescent probes with different affinities to a number of reactive species. The analysis and quantification of EPR spectra revealed the formation of enormous amounts of ·OH radicals using Ar-CAP compared with that by X-irradiation. Very small amounts of H atoms were detected whereas nitric oxide was not found. The formation of ·OH radicals depended on the type of rare gas used and the yield correlated inversely with ionization energy in the order of krypton > argon = neon > helium. No pyrolysis radicals were detected in aqueous solutions exposed to Ar-CAP. Intracellularly, ·OH, H2O2, which is the recombination product of ·OH, and OCl- were the most likely formed reactive oxygen species after exposure to Ar-CAP. Intracellularly, there was no practical evidence for the formation of NO whereas very small amounts of superoxides were formed. Despite the superiority of Ar-CAP in forming ·OH radicals, the exposure to X-rays proved more lethal. The mechanism of free radical formation in aqueous solutions and an
Uchiyama, Hidefumi; Zhao, Qing-Li; Hassan, Mariame Ali; Andocs, Gabor; Nojima, Nobuyuki; Takeda, Keigo; Ishikawa, Kenji; Hori, Masaru; Kondo, Takashi
2015-01-01
Electron paramagnetic resonance (EPR)-spin trapping and flow cytometry were used to identify free radicals generated using argon-cold atmospheric plasma (Ar-CAP) in aqueous solutions and intracellularly in comparison with those generated by X-irradiation. Ar-CAP was generated using a high-voltage power supply unit with low-frequency excitation. The characteristics of Ar-CAP were estimated by vacuum UV absorption and emission spectra measurements. Hydroxyl (·OH) radicals and hydrogen (H) atoms in aqueous solutions were identified with the spin traps 5,5-dimethyl-1-pyrroline N-oxide (DMPO), 3,3,5,5-tetramethyl-1-pyrroline-N-oxide (M4PO), and phenyl N-t-butylnitrone (PBN). The occurrence of Ar-CAP-induced pyrolysis was evaluated using the spin trap 3,5-dibromo-4-nitrosobenzene sulfonate (DBNBS) in aqueous solutions of DNA constituents, sodium acetate, and L-alanine. Human lymphoma U937 cells were used to study intracellular oxidative stress using five fluorescent probes with different affinities to a number of reactive species. The analysis and quantification of EPR spectra revealed the formation of enormous amounts of ·OH radicals using Ar-CAP compared with that by X-irradiation. Very small amounts of H atoms were detected whereas nitric oxide was not found. The formation of ·OH radicals depended on the type of rare gas used and the yield correlated inversely with ionization energy in the order of krypton > argon = neon > helium. No pyrolysis radicals were detected in aqueous solutions exposed to Ar-CAP. Intracellularly, ·OH, H2O2, which is the recombination product of ·OH, and OCl- were the most likely formed reactive oxygen species after exposure to Ar-CAP. Intracellularly, there was no practical evidence for the formation of NO whereas very small amounts of superoxides were formed. Despite the superiority of Ar-CAP in forming ·OH radicals, the exposure to X-rays proved more lethal. The mechanism of free radical formation in aqueous solutions and an
NASA Astrophysics Data System (ADS)
Afzali, Arezoo; Mottaghitalab, Vahid; Seyyed Afghahi, Seyyed Salman; Jafarian, Mojtaba; Atassi, Yomen
2017-11-01
Current investigation focuses on the electromagnetic properties of nonwoven fabric coated with BaFe12O19 (BHF) /MWCNTs/PANi nanocomposite in X and Ku bands. The BHF/MWCNTs and BHF/MWCNTs/PANi nanocomposites are prepared using the sol gel and in-situ polymerization methods respectively. The absorbent fabric was prepared based on applying a 40 wt% of BHF/MWCNTs/PANi nanocomposite in silicon resin on nonwoven fabric via roller coating technique The X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM) and vector network analysis (VNA) are used to peruse microstructural, magnetic and electromagnetic features of the composite and absorber fabric respectively. The microscopic images of the fabric coated with magnetic nanocomposite shows a homogenous layer of nanoparticles on the fabric surface. The maximum reflection loss of binary nano-composite BHF/MWCNTs was measured about -28.50 dB at 11.72 GHz with 1.7 GHz bandwidth (RL < -10 dB) in X band. Moreover in Ku band, the maximum reflection loss is -29.66 dB at 15.78 GHz with 3.2 GHz bandwidths. Also the ternary nanocomposite BHF/MWCNTs/PANi exhibits a broad band absorber over a wide range of X band with a maximum reflection loss of -36.2 dB at 10.2 GHz with 1.5 GHz bandwidth and in the Ku band has arrived a maximum reflection loss of -37.65 dB at 12.84 GHz with 2.43 GHz bandwidth. This result reflects the synergistic effect of the different components with different loss mechanisms. As it is observed due to the presence of PANi in the structure of nanocomposite, the amount of absorption has increased extraordinarily. The absorber fabric exhibits a maximum reflection loss of -24.2 dB at 11.6 GHz with 4 GHz bandwidth in X band. However, in Ku band, the absorber fabric has had the maximum absorption in 16.88 GHz that is about -24.34 dB with 6 GHz bandwidth. Therefore, results indicate that the fabric samples coated represents appreciable maximum absorption value of more than 99% in
Islam, M T; Samsuzzaman, M
2014-01-01
This paper introduces a new configuration of compact, triangular- and diamond-slotted, microstrip-fed, low-profile antenna for C/X band applications on polytetrafluoroethylene glass microfiber reinforced material substrate. The antenna is composed of a rectangular-shaped patch containing eight triangles and two diamond-shaped slots and an elliptical-slotted ground plane. The rectangular-shaped patch is obtained by cutting two diamond slots in the middle of the rectangular patch, six triangular slots on the left and right side of the patch, and two triangular slots on the up and down side of the patch. The slotted radiating patch, the elliptical-slotted ground plane, and the microstrip feed enable the matching bandwidth to be widened. A prototype of the optimized antenna was fabricated on polytetrafluoroethylene glass microfiber reinforced material substrate using LPKF prototyping machine and investigated to validate the proposed design. The simulated results are compared with the measured data, and good agreement is achieved. The proposed antenna offers fractional bandwidths of 13.69% (7.78-8.91 GHz) and 10.35% (9.16-10.19 GHz) where S11 < -10 dB at center frequencies of 8.25 GHz and 9.95 GHz, respectively, and relatively stable gain, good radiation efficiency, and omnidirectional radiation patterns in the matching band.
X-ray source development for EXAFS measurements on the National Ignition Facility
Coppari, F.; Thorn, D. B.; Kemp, G. E.; ...
2017-08-28
We present that extended X-ray absorption Fine Structure (EXAFS) measurements require a bright, spectrally smooth, and broad-band x-ray source. In a laser facility, such an x-ray source can be generated by a laser-driven capsule implosion. In order to optimize the x-ray emission, different capsule types and laser irradiations have been tested at the National Ignition Facility (NIF). A crystal spectrometer is used to disperse the x-rays and high efficiency image plate detectors are used to measure the absorption spectra in transmission geometry. Finally, EXAFS measurements at the K-edge of iron at ambient conditions have been obtained for the first timemore » on the NIF laser, and the requirements for optimization have been established.« less
Hands-on work fine-tunes X-band PIN-diode duplexer
NASA Astrophysics Data System (ADS)
Schneider, P.
1985-06-01
Computer-aided design (CAD) programs for fabricating PIN-diode duplexers are useful in avoiding time-consuming cut-and-try techniques. Nevertheless, to attain minimum insertion loss, only experimentation yields the optimum microstrip circuitry. A PIN-diode duplexer, consisting of two SPST PIN-diode switches and a pair of 3-dB Lange microstrip couplers, designed for an X-band transmit/receive module exemplifies what is possible when computer-derived designs and experimentation are used together. Differences between the measured and computer-generated figures for insertion loss can be attributed to several factors not included in the CAD program - for example, radiation and connector losses. Mechanical tolerances of the microstrip PC board and variations in the SMA connector-to-microstrip transition contribute to the discrepancy.
Vestad, Tor Arne; Malinen, Eirik; Olsen, Dag Rune; Hole, Eli Olaug; Sagstuen, Einar
2004-10-21
Solid-state radiation dosimetry by electron paramagnetic resonance (EPR) spectroscopy and thermoluminescence (TL) was utilized for the determination of absorbed doses in the range of 0.5-2.5 Gy. The dosimeter materials used were lithium formate and lithium fluoride (TLD-100 rods) for EPR dosimetry and TL dosimetry, respectively. 60Co gamma-rays and 4, 6, 10 and 15 MV x-rays were employed. The main objectives were to compare the variation in dosimeter reading of the respective dosimetry systems and to determine the photon energy dependence of the two dosimeter materials. The EPR dosimeter sensitivity was constant over the dose range in question, while the TL sensitivity increased by more than 5% from 0.5 to 2.5 Gy, thus displaying a supralinear dose response. The average relative standard deviation in the dosimeter reading per dose was 3.0% and 1.2% for the EPR and TL procedures, respectively. For EPR dosimeters, the relative standard deviation declined significantly from 4.3% to 1.1% over the dose range in question. The dose-to-water energy response for the megavoltage x-ray beams relative to 60Co gamma-rays was in the range of 0.990-0.979 and 0.984-0.962 for lithium formate and lithium fluoride, respectively. The results show that EPR dosimetry with lithium formate provides dose estimates with a precision comparable to that of TL dosimetry (using lithium fluoride) for doses above 2 Gy, and that lithium formate is slightly less dependent on megavoltage photon beam energy than lithium fluoride.
NASA Astrophysics Data System (ADS)
Vestad, Tor Arne; Malinen, Eirik; Rune Olsen, Dag; Olaug Hole, Eli; Sagstuen, Einar
2004-10-01
Solid-state radiation dosimetry by electron paramagnetic resonance (EPR) spectroscopy and thermoluminescence (TL) was utilized for the determination of absorbed doses in the range of 0.5-2.5 Gy. The dosimeter materials used were lithium formate and lithium fluoride (TLD-100 rods) for EPR dosimetry and TL dosimetry, respectively. 60Co ggr-rays and 4, 6, 10 and 15 MV x-rays were employed. The main objectives were to compare the variation in dosimeter reading of the respective dosimetry systems and to determine the photon energy dependence of the two dosimeter materials. The EPR dosimeter sensitivity was constant over the dose range in question, while the TL sensitivity increased by more than 5% from 0.5 to 2.5 Gy, thus displaying a supralinear dose response. The average relative standard deviation in the dosimeter reading per dose was 3.0% and 1.2% for the EPR and TL procedures, respectively. For EPR dosimeters, the relative standard deviation declined significantly from 4.3% to 1.1% over the dose range in question. The dose-to-water energy response for the megavoltage x-ray beams relative to 60Co ggr-rays was in the range of 0.990-0.979 and 0.984-0.962 for lithium formate and lithium fluoride, respectively. The results show that EPR dosimetry with lithium formate provides dose estimates with a precision comparable to that of TL dosimetry (using lithium fluoride) for doses above 2 Gy, and that lithium formate is slightly less dependent on megavoltage photon beam energy than lithium fluoride.
Nano-crystalline Magnesium Substituted Cadmium Ferrites as X-band Microwave Absorbers
NASA Astrophysics Data System (ADS)
Bhongale, S. R.; Ingawale, H. R.; Shinde, T. J.; Pubby, Kunal; Bindra Narang, Sukhleen; Vasambekar, P. N.
2017-11-01
The magnetic and electromagnetic properties of nanocrystalline spinel ferrites with chemical formula MgxCd1-xFe2O4 (x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) prepared by oxalate co-precipitation method under microwave sintering technique were studied. The magnetic and dielectric parameters of ferrites were determined by using vibrating sample magnetometer (VSM) and vector network analyzer (VNA) respectively. Magnetic parameters such as saturation magnetizations (Ms), coercive force (Hc), remnant magnetization (Mr), Yafet-Kittel (Y-K) angle of ferrites were determined from hysteresis loops. The variation of real permittivity (ε‧), dielectric loss tangent (tanδe), real permeability (μ‧) and magnetic loss tangent (tanδm) with frequency and Mg2+content were studied in X-band frequency range. The values of ε‧, tanδe, μ‧ and tanδm of ferrites were observed to be in range of 4.2 - 6.12, 2.9 × 10-1 - 6 × 10-2, 0.6 - 1.12 and 4.5 × 10-1 - 2 × 10-3 respectively for the prepared compositions. The study of variation of reflection loss with frequency of all ferrites shows that ferrite with magnesium content x = 0.4 can be potential candidate for microwave applications in X-band.
Full cycle rapid scan EPR deconvolution algorithm.
Tseytlin, Mark
2017-08-01
Rapid scan electron paramagnetic resonance (RS EPR) is a continuous-wave (CW) method that combines narrowband excitation and broadband detection. Sinusoidal magnetic field scans that span the entire EPR spectrum cause electron spin excitations twice during the scan period. Periodic transient RS signals are digitized and time-averaged. Deconvolution of absorption spectrum from the measured full-cycle signal is an ill-posed problem that does not have a stable solution because the magnetic field passes the same EPR line twice per sinusoidal scan during up- and down-field passages. As a result, RS signals consist of two contributions that need to be separated and postprocessed individually. Deconvolution of either of the contributions is a well-posed problem that has a stable solution. The current version of the RS EPR algorithm solves the separation problem by cutting the full-scan signal into two half-period pieces. This imposes a constraint on the experiment; the EPR signal must completely decay by the end of each half-scan in order to not be truncated. The constraint limits the maximum scan frequency and, therefore, the RS signal-to-noise gain. Faster scans permit the use of higher excitation powers without saturating the spin system, translating into a higher EPR sensitivity. A stable, full-scan algorithm is described in this paper that does not require truncation of the periodic response. This algorithm utilizes the additive property of linear systems: the response to a sum of two inputs is equal the sum of responses to each of the inputs separately. Based on this property, the mathematical model for CW RS EPR can be replaced by that of a sum of two independent full-cycle pulsed field-modulated experiments. In each of these experiments, the excitation power equals to zero during either up- or down-field scan. The full-cycle algorithm permits approaching the upper theoretical scan frequency limit; the transient spin system response must decay within the scan
Full cycle rapid scan EPR deconvolution algorithm
NASA Astrophysics Data System (ADS)
Tseytlin, Mark
2017-08-01
Rapid scan electron paramagnetic resonance (RS EPR) is a continuous-wave (CW) method that combines narrowband excitation and broadband detection. Sinusoidal magnetic field scans that span the entire EPR spectrum cause electron spin excitations twice during the scan period. Periodic transient RS signals are digitized and time-averaged. Deconvolution of absorption spectrum from the measured full-cycle signal is an ill-posed problem that does not have a stable solution because the magnetic field passes the same EPR line twice per sinusoidal scan during up- and down-field passages. As a result, RS signals consist of two contributions that need to be separated and postprocessed individually. Deconvolution of either of the contributions is a well-posed problem that has a stable solution. The current version of the RS EPR algorithm solves the separation problem by cutting the full-scan signal into two half-period pieces. This imposes a constraint on the experiment; the EPR signal must completely decay by the end of each half-scan in order to not be truncated. The constraint limits the maximum scan frequency and, therefore, the RS signal-to-noise gain. Faster scans permit the use of higher excitation powers without saturating the spin system, translating into a higher EPR sensitivity. A stable, full-scan algorithm is described in this paper that does not require truncation of the periodic response. This algorithm utilizes the additive property of linear systems: the response to a sum of two inputs is equal the sum of responses to each of the inputs separately. Based on this property, the mathematical model for CW RS EPR can be replaced by that of a sum of two independent full-cycle pulsed field-modulated experiments. In each of these experiments, the excitation power equals to zero during either up- or down-field scan. The full-cycle algorithm permits approaching the upper theoretical scan frequency limit; the transient spin system response must decay within the scan
Wang, Qiang; Barclay, J Elaine; Blake, Alexander J; Davies, E Stephen; Evans, David J; Marr, Andrew C; McInnes, Eric J L; McMaster, Jonathan; Wilson, Claire; Schröder, Martin
2004-07-19
A novel [NiS4Fe2(CO)6]cluster (1: 'S(4)'=(CH(3)C(6)H(3)S(2))(2)(CH(2))(3)) has been synthesised, structurally characterised and has been shown to undergo a chemically reversible reduction process at -1.31 V versus Fc(+)/Fc to generate the EPR-active monoanion 1(-). Multifrequency Q-, X- and S-band EPR spectra of (61)Ni-enriched 1(-) show a well-resolved quartet hyperfine splitting in the low-field region due to the interaction with a single (61)Ni (I=3/2) nucleus. Simulations of the EPR spectra require the introduction of a single angle of non-coincidence between g(1) and A(1), and g(3) and A(3) to reproduce all of the features in the S- and X-band spectra. This behaviour provides a rare example of the detection and measurement of non-coincidence effects from frozen-solution EPR spectra without the need for single-crystal measurements, and in which the S-band experiment is sensitive to the non-coincidence. An analysis of the EPR spectra of 1(-) reveals a 24 % Ni contribution to the SOMO in 1(-), supporting a delocalisation of the spin-density across the NiFe(2) cluster. This observation is supported by IR spectroscopic results which show that the CO stretching frequencies, nu(CO), shift to lower frequency by about 70 cm(-1) when 1 is reduced to 1(-). Density functional calculations provide a framework for the interpretation of the spectroscopic properties of 1(-) and suggest that the SOMO is delocalised over the whole cluster, but with little S-centre participation. This electronic structure contrasts with that of the Ni-A, -B, -C and -L forms of [NiFe] hydrogenase in which there is considerable S participation in the SOMO.
Complete multipactor suppression in an X-band dielectric-loaded accelerating structure
DOE Office of Scientific and Technical Information (OSTI.GOV)
Jing, C.; Gold, S. H.; Fischer, Richard
2016-05-09
Multipactor is a major issue limiting the gradient of rf-driven Dielectric-Loaded Accelerating (DLA) structures. Theoretical models have predicted that an axial magnetic field applied to DLA structures may completely block the multipactor discharge. However, previous attempts to demonstrate this magnetic field effect in an X-band traveling-wave DLA structure were inconclusive, due to the axial variation of the applied magnetic field, and showed only partial suppression of the multipactor loading [Jing et al., Appl. Phys. Lett. 103, 213503 (2013)]. The present experiment has been performed under improved conditions with a uniform axial magnetic field extending along the length of an X-bandmore » standing-wave DLA structure. Multipactor loading began to be continuously reduced starting from 3.5 kG applied magnetic field and was completely suppressed at 8 kG. Dependence of multipactor suppression on the rf gradient inside the DLA structure was also measured.« less
Kripal, Ram; Pandey, Sangita
2010-06-01
The electron paramagnetic resonance (EPR) studies are carried out on Cr(3+) ion doped ammonium dihydrogen phosphate (ADP) single crystals at room temperature. Four magnetically inequivalent sites for chromium are observed. No hyperfine structure is obtained. The crystal-field and spin Hamiltonian parameters are calculated from the resonance lines obtained at different angular rotations. The zero field and spin Hamiltonian parameters of Cr(3+) ion in ADP are calculated as: |D|=(257+/-2) x 10(-4) cm(-1), |E|=(79+/-2) x 10(-4) cm(-1), g=1.9724+/-0.0002 for site I; |D|=(257+/-2) x 10(-4) cm(-1), |E|=(77+/-2) x 10(-4) cm(-1), g=1.9727+/-0.0002 for site II; |D|=(259+/-2) x 10(-4) cm(-1), |E|=(78+/-2) x 10(-4) cm(-1), g=1.9733+/-0.0002 for site III; |D|=(259+/-2) x 10(-4) cm(-1), |E|=(77+/-2) x 10(-4) cm(-1), g=1.973+/-0.0002 for site IV, respectively. The site symmetry of Cr(3+) doped single crystal is discussed on the basis of EPR data. The Cr(3+) ion enters the lattice substitutionally replacing the NH(4)(+) sites. The optical absorption spectra are recorded in 195-925 nm wavelength range at room temperature. The energy values of different orbital levels are determined. On the basis of EPR and optical data, the nature of bonding in the crystal is discussed. The calculated values of Racah interelectronic repulsion parameters (B and C), cubic crystal-field splitting parameter (D(q)) and nephelauxetic parameters (h and k) are: B=640, C=3070, D(q)=2067 cm(-1), h=1.44 and k=0.21, respectively. ZFS parameters are also determined using B(kq) parameters from superposition model. Copyright 2010 Elsevier B.V. All rights reserved.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Bahar, N; Roberts, K; Stabile, F
Purpose: Medical intervention following a major, unplanned radiation event can elevate the human whole body exposure LD50 from 3 to 7 Gy. On a large scale, intervention cannot be achieved effectively without accurate and efficient triage. Current methods of retrospective biodosimetry are restricted in capability and applicability; published human data is limited. We aim to further develop, validate, and optimize an automated field-deployable in vivo electron paramagnetic resonance (EPR) instrument that can fill this need. Methods: Ionizing radiation creates highly-stable, carbonate-based free radicals within tooth enamel. Using a process similar to nuclear magnetic resonance, EPR directly measures the presence ofmore » radiation-induced free radicals. We performed baseline EPR measurements on one of the upper central incisors of total body irradiation (TBI) and head and neck (H&N) radiotherapy patients before their first treatment. Additional measurements were performed between subsequent fractions to examine the EPR response with increasing radiation dose. Independent dosimetry measurements were performed with optically-stimulated luminescent dosimeters (OSLDs) and diodes to more accurately establish the relationship between EPR signal and delivered radiation dose. Results: 36 EPR measurements were performed over the course of four months on two TBI and four H & N radiotherapy patients. We observe a linear increase in EPR signal with increasing dose across the entirety of the tested range. A linear least squares-weighted fit of delivered dose versus measured signal amplitude yields an adjusted R-square of 0.966. The standard error of inverse prediction (SEIP) is 1.77 Gy. For doses up to 7 Gy, the range most relevant to triage, we calculate an SEIP of 1.29 Gy. Conclusion: EPR spectroscopy provides a promising method of retrospective, non-invasive, in vivo biodosimetry. Our preliminary data show an excellent correlation between predicted signal amplitude and
Adiabatic and fast passage ultra-wideband inversion in pulsed EPR.
Doll, Andrin; Pribitzer, Stephan; Tschaggelar, René; Jeschke, Gunnar
2013-05-01
We demonstrate that adiabatic and fast passage ultra-wideband (UWB) pulses can achieve inversion over several hundreds of MHz and thus enhance the measurement sensitivity, as shown by two selected experiments. Technically, frequency-swept pulses are generated by a 12 GS/s arbitrary waveform generator and upconverted to X-band frequencies. This pulsed UWB source is utilized as an incoherent channel in an ordinary pulsed EPR spectrometer. We discuss experimental methodologies and modeling techniques to account for the response of the resonator, which can strongly limit the excitation bandwidth of the entire non-linear excitation chain. Aided by these procedures, pulses compensated for bandwidth or variations in group delay reveal enhanced inversion efficiency. The degree of bandwidth compensation is shown to depend critically on the time available for excitation. As a result, we demonstrate optimized inversion recovery and double electron electron resonance (DEER) experiments. First, virtually complete inversion of the nitroxide spectrum with an adiabatic pulse of 128ns length is achieved. Consequently, spectral diffusion between inverted and non-inverted spins is largely suppressed and the observation bandwidth can be increased to increase measurement sensitivity. Second, DEER is performed on a terpyridine-based copper (II) complex with a nitroxide-copper distance of 2.5nm. As previously demonstrated on this complex, when pumping copper spins and observing nitroxide spins, the modulation depth is severely limited by the excitation bandwidth of the pump pulse. By using fast passage UWB pulses with a maximum length of 64ns, we achieve up to threefold enhancement of the modulation depth. Associated artifacts in distance distributions when increasing the bandwidth of the pump pulse are shown to be small. Copyright © 2013 Elsevier Inc. All rights reserved.
NASA Astrophysics Data System (ADS)
Andersson, K. Kristoffer; Barra, Anne-Laure
2002-04-01
Low temperature electron paramagnetic resonance (EPR) spectroscopy with frequencies between 95 and 345 GHz and magnetic fields up to 12 T have been used to study radicals and metal sites in proteins and small inorganic model complexes. We have studied radicals, Fe, Cu and Mn containing proteins. For S=1/2 systems, the high frequency method can resolve the g-value anisotropy. It was used in mouse ribonucleotide reductase (RNR) to show the presence of a hydrogen bond to the tyrosyl radical oxygen. At 285 GHz the type 2 Cu(II) signal in the complex enzyme laccase is clearly resolved from the Hg(II) containing laccase peroxide adduct. For simple metal sites, the systems over S=1/2 can be described by the spin Hamiltonian: HS= BgS+ D[ Sz2- S( S+1)/3+ E/ D ( Sx2- Sy2)]. From the high frequency EPR the D-value can be determined directly by, (I) shifts of geff for half-integer spin systems with large D-values as observed at 345 GHz on an Fe(II)NOEDTA complex, which is best described as S=3/2 system with D=11.5 cm -1, E=0.1 cm -1 and gx= gy= gz=2.0; (II) measuring the outermost signal, for systems with small D values, distant of (2 S-1)*∣ D∣ from the center of the spectrum as observed in S=5/2 Fe(III)EDTA. In Mn(II) substituted mouse RNR R2 protein the weakly interacting Mn(II) at X-band could be observed as decoupled Mn(II) at 285 GHz.
Origin of band gap bowing in dilute GaAs1-xNx and GaP1-xNx alloys: A real-space view
NASA Astrophysics Data System (ADS)
Virkkala, Ville; Havu, Ville; Tuomisto, Filip; Puska, Martti J.
2013-07-01
The origin of the band gap bowing in dilute nitrogen doped gallium based III-V semiconductors is largely debated. In this paper we show the dilute GaAs1-xNx and GaP1-xNx as representative examples that the nitrogen-induced states close to the conduction band minimum propagate along the zigzag chains on the {110} planes. Thereby states originating from different N atoms interact with each other resulting in broadening of the nitrogen-induced states which narrows the band gap. Our modeling based on ab initio theoretical calculations explains the experimentally observed N concentration dependent band gap narrowing both qualitatively and quantitatively.
Characterization of Mediterranean hail-bearing storms using an operational polarimetric X-band radar
NASA Astrophysics Data System (ADS)
Vulpiani, G.; Baldini, L.; Roberto, N.
2015-07-01
This work documents the fruitul use of X-band radar observations for the monitoring of severe storms in an operational framework. More specifically, a couple of severe hail-bearing Mediterranean storms occurred in 2013 in southern Italy, flooding two important cities of Sicily, are described in terms of their polarimetric radar signatures and retrieved rainfall fields. It is used the X-band dual-polarization radar operating inside the Catania airport (Sicily, Italy), managed by the Italian Department of Civil Protection. A suitable processing is applied to X-band radar measurements. The crucial procedural step relies on the differential phase processing based on an iterative approach that uses a very short-length (1 km) moving window allowing to properly catch the observed high radial gradients of the differential phase. The parameterization of the attenuation correction algorithm, which use the reconstructed differential phase shift, is derived from electromagnetic simulations based on 3 years of DSD observations collected in Rome (Italy). A Fuzzy Logic hydrometeor classification algorithm was also adopted to support the analysis of the storm characteristics. The precipitation fields amount were reconstructed using a combined polarimetric rainfall algorithm based on reflectivity and specific differential phase. The first considered storm was observed on the 21 February, when a winter convective system, originated in the Tyrrhenian sea, hit only marginally the central-eastern coastline of Sicily causing the flash-flood of Catania. Due to the optimal radar location (the system is located at just few kilometers from the city center), it was possible to well retrieve the storm characteristics, including the amount of rainfall field at ground. Extemporaneous signal extinction, caused by close-range hail core causing significant differential phase shift in very short range path, is documented. The second storm, occurred on 21 August 2013, is a summer mesoscale
EPR investigations of gamma-irradiated ground black pepper
NASA Astrophysics Data System (ADS)
Polovka, Martin; Brezová, Vlasta; Staško, Andrej; Mazúr, Milan; Suhaj, Milan; Šimko, Peter
2006-02-01
The γ-radiation treatment of ground black pepper samples resulted in the production of three paramagnetic species ( GI- GIII) which arise from a different origin and have different thermal behavior and stability. The axially symmetric spectra can be characterized by the spin Hamiltonian parameters: GI ( g⊥=2.0060, g∥=2.0032; A⊥=0.85 mT, A∥=0.70 mT) and GII ( g⊥=2.0060, g∥=2.0050; A⊥=0.50 mT, A∥=0.40 mT) assigned to carbohydrate radical structures. The parameters of EPR signal GIII ( g⊥=2.0029, g∥=2.0014; A⊥=3.00 mT, A∥=1.80 mT) possessed features characteristic of cellulose radical species. The activation energies, evaluated by Arrhenius analysis, are in order Ea( GI)< Ea( GIII)< Ea( GII). The EPR measurements performed 20 weeks after radiation process confirmed that a temperature increase from 298 to 353 K, caused a significant decrease of integral EPR signal intensity for γ-irradiated samples (˜40%), compared to the reference (non-irradiated) ground black pepper, where a decrease of ˜13% was found. The influence of γ-radiation treatment on the radical-scavenging activities of aqueous and ethanol extracts of black pepper were investigated by both an EPR spin trapping technique and DPPH assay. No changes were detected in either the water or ethanol extracts for a γ-irradiation dose of 10 kGy.
NASA Technical Reports Server (NTRS)
Wintucky, Edwin G.; Simons, Rainee N.
2015-01-01
This paper presents the design, fabrication and test results for a novel waveguide multimode directional coupler (MDC). The coupler, fabricated from two dissimilar frequency band waveguides, is capable of isolating power at the second harmonic frequency from the fundamental power at the output port of a traveling-wave tube (TWT) amplifier. Test results from proof-of-concept demonstrations are presented for a Ku-band/Ka-band MDC and a Ka-band/E-band MDC. In addition to power measurements at harmonic frequencies, a potential application of the MDC is in the design of a satellite borne beacon source for atmospheric propagation studies at millimeter-wave (mm-wave) frequencies (Ka-band and E-band).
A discussion on the use of X-band SAR images in marine applications
NASA Astrophysics Data System (ADS)
Schiavulli, D.; Sorrentino, A.; Migliaccio, M.
2012-10-01
The Synthetic Aperture Radar (SAR) is able to generate images of the sea surface that can be exploited to extract geophysical information of environmental interest. In order to enhance the operational use of these data in the marine applications the revisit time is to be improved. This goal can be achieved by using SAR virtual or real constellations and/or exploiting new antenna technologies that allow huge swath and fine resolution. Within this framework, the presence of the Italian and German X-band SAR constellations is of special interest while the new SAR technologies are not nowadays operated. Although SAR images are considered to be independent of weather conditions, this is only partially true at higher frequencies, e.g. X-band. In fact, observations can present signature corresponding to high intensity precipitating clouds, i.e. rain cells. Further, ScanSAR images may be characterized by the presence of processing artifacts, called scalloping, that corrupt image interpretation. In this paper we review these key facts that are at the basis of an effective use of X-band SAR images for marine applications.
Pulsed-High Field/High-Frequency EPR Spectroscopy
NASA Astrophysics Data System (ADS)
Fuhs, Michael; Moebius, Klaus
Pulsed high-field/high-frequency electron paramagnetic resonance (EPR) spectroscopy is used to disentangle many kinds of different effects often obscured in continuous wave (cw) EPR spectra at lower magnetic fields/microwave frequencies. While the high magnetic field increases the resolution of G tensors and of nuclear Larmor frequencies, the high frequencies allow for higher time resolution for molecular dynamics as well as for transient paramagnetic intermediates studied with time-resolved EPR. Pulsed EPR methods are used for example for relaxation-time studies, and pulsed Electron Nuclear DOuble Resonance (ENDOR) is used to resolve unresolved hyperfine structure hidden in inhomogeneous linewidths. In the present article we introduce the basic concepts and selected applications to structure and mobility studies on electron transfer systems, reaction centers of photosynthesis as well as biomimetic models. The article concludes with an introduction to stochastic EPR which makes use of an other concept for investigating resonance systems in order to increase the excitation bandwidth of pulsed EPR. The limited excitation bandwidth of pulses at high frequency is one of the main limitations which, so far, made Fourier transform methods hardly feasible.
Membrane remodeling by amyloidogenic and non-amyloidogenic proteins studied by EPR.
Varkey, Jobin; Langen, Ralf
2017-07-01
The advancement in site-directed spin labeling of proteins has enabled EPR studies to expand into newer research areas within the umbrella of protein-membrane interactions. Recently, membrane remodeling by amyloidogenic and non-amyloidogenic proteins has gained a substantial interest in relation to driving and controlling vital cellular processes such as endocytosis, exocytosis, shaping of organelles like endoplasmic reticulum, Golgi and mitochondria, intracellular vesicular trafficking, formation of filopedia and multivesicular bodies, mitochondrial fusion and fission, and synaptic vesicle fusion and recycling in neurotransmission. Misregulation in any of these processes due to an aberrant protein (mutation or misfolding) or alteration of lipid metabolism can be detrimental to the cell and cause disease. Dissection of the structural basis of membrane remodeling by proteins is thus quite necessary for an understanding of the underlying mechanisms, but it remains a formidable task due to the difficulties of various common biophysical tools in monitoring the dynamic process of membrane binding and bending by proteins. This is largely since membranes generally complicate protein structure analysis and this problem is amplified for structural analysis in the presence of different types of membrane curvatures. Recent EPR studies on membrane remodeling by proteins show that a significant structural information can be generated to delineate the role of different protein modules, domains and individual amino acids in the generation of membrane curvature. These studies also show how EPR can complement the data obtained by high resolution techniques such as X-ray and NMR. This perspective covers the application of EPR in recent studies for understanding membrane remodeling by amyloidogenic and non-amyloidogenic proteins that is useful for researchers interested in using or complimenting EPR to gain better understanding of membrane remodeling. We also discuss how a single
Membrane remodeling by amyloidogenic and non-amyloidogenic proteins studied by EPR
NASA Astrophysics Data System (ADS)
Varkey, Jobin; Langen, Ralf
2017-07-01
The advancement in site-directed spin labeling of proteins has enabled EPR studies to expand into newer research areas within the umbrella of protein-membrane interactions. Recently, membrane remodeling by amyloidogenic and non-amyloidogenic proteins has gained a substantial interest in relation to driving and controlling vital cellular processes such as endocytosis, exocytosis, shaping of organelles like endoplasmic reticulum, Golgi and mitochondria, intracellular vesicular trafficking, formation of filopedia and multivesicular bodies, mitochondrial fusion and fission, and synaptic vesicle fusion and recycling in neurotransmission. Misregulation in any of these processes due to an aberrant protein (mutation or misfolding) or alteration of lipid metabolism can be detrimental to the cell and cause disease. Dissection of the structural basis of membrane remodeling by proteins is thus quite necessary for an understanding of the underlying mechanisms, but it remains a formidable task due to the difficulties of various common biophysical tools in monitoring the dynamic process of membrane binding and bending by proteins. This is largely since membranes generally complicate protein structure analysis and this problem is amplified for structural analysis in the presence of different types of membrane curvatures. Recent EPR studies on membrane remodeling by proteins show that a significant structural information can be generated to delineate the role of different protein modules, domains and individual amino acids in the generation of membrane curvature. These studies also show how EPR can complement the data obtained by high resolution techniques such as X-ray and NMR. This perspective covers the application of EPR in recent studies for understanding membrane remodeling by amyloidogenic and non-amyloidogenic proteins that is useful for researchers interested in using or complimenting EPR to gain better understanding of membrane remodeling. We also discuss how a single
Zn(x)Cd(1-x)Se nanomultipods with tunable band gaps: synthesis and first-principles calculations.
Wei, Hao; Su, Yanjie; Han, Ziyi; Li, Tongtong; Ren, Xinglong; Yang, Zhi; Wei, Liangming; Cong, Fengsong; Zhang, Yafei
2013-06-14
In this paper, we demonstrate that ZnxCd1-xSe nanomultipods can be synthesized via a facile and nontoxic solution-based method. Interesting aspects of composition, morphology and optical properties were deeply explored. The value of Zn/(Zn+Cd) could be altered across the entire range from 0.08 to 0.86 by varying the ratio of cation precursor contents. The band gap energy could be linearly tuned from 1.88 to 2.48 eV with respect to the value of Zn/(Zn+Cd). The experiment also showed that oleylamine played a dominant role in the formation of multipod structure. A possible growth mechanism was further suggested. First-principles calculations of band gap energy and density of states in the Vienna ab initio simulation package code were performed to verify the experimental variation tendency of the band gap. Computational results indicated that dissimilarities of electronic band structures and orbital constitutions determined the tunable band gap of the as-synthesized nanomultipod, which might be promising for versatile applications in relevant areas of solar cells, biomedicine, sensors, catalysts and so on.
Chen, Lei; Cui, Hui-Hui; Stavretis, Shelby E.; ...
2016-12-07
We synthesized and studied three mononuclear cobalt(II) tetranitrate complexes (A) 2[Co(NO 3) 4] with different countercations, Ph 4P + (1), MePh 3P + (2), and Ph 4As + (3), using X-ray single-crystal diffraction, magnetic measurements, inelastic neutron scattering (INS), high-frequency and high-field EPR (HF-EPR) spectroscopy, and theoretical calculations. Furthermore, the X-ray diffraction studies reveal that the structure of the tetranitrate cobalt anion varies with the countercation. 1 and 2 exhibit highly irregular seven-coordinate geometries, while the central Co(II) ion of 3 is in a distorted-dodecahedral configuration. The sole magnetic transition observed in the INS spectroscopy of 1–3 corresponds to themore » zero-field splitting (2(D 2 + 3E 2) 1/2) from 22.5(2) cm –1 in 1 to 26.6(3) cm –1 in 2 and 11.1(5) cm –1 in 3. The positive sign of the D value, and hence the easy-plane magnetic anisotropy, was demonstrated for 1 by INS studies under magnetic fields and HF-EPR spectroscopy. The combined analyses of INS and HF-EPR data yield the D values as +10.90(3), +12.74(3), and +4.50(3) cm –1 for 1–3, respectively. Frequency- and temperature-dependent alternating-current magnetic susceptibility measurements reveal the slow magnetization relaxation in 1 and 2 at an applied dc field of 600 Oe, which is a characteristic of field-induced single-molecule magnets (SMMs). Finally, the electronic structures and the origin of magnetic anisotropy of 1–3 were revealed by calculations at the CASPT2/NEVPT2 level.« less
Yan, Lifen; Dapper, Christie H.; Scott, Aubrey D.; Newton, William E.
2015-01-01
We have used Fourier transform infrared spectroscopy (FT-IR) to observe the photolysis and recombination of a novel EPR-silent CO-inhibited form of α-H195Q nitrogenase from Azotobacter vinelandii. Photolysis at 4 K yields a strong negative IR difference band at 1938 cm−1, along with a weaker negative feature at 1911 cm−1. These bands and the associated chemical species have both been assigned the label ‘Hi-3’. A positive band at 1921 cm−1 is assigned to the ‘Lo-3’ photoproduct. By using an isotopic mixture of 12C16O and 13C18O, we show that the Hi-3 bands arise from coupling of two similar CO oscillators with one uncoupled frequency at ~1917 cm−1. Although in previous studies Lo-3 was not observed to recombine, by extending the observation range to 200–240 K we found that recombination to Hi-3 does indeed occur, with an activation energy of ~6.5 kJ mol−1. The frequencies of the Hi-3 bands suggest terminal CO ligation. We tested this hypothesis with DFT calculations on models with terminal CO ligands on Fe2 and Fe6 of the FeMo-cofactor. An S = 0 model with both CO ligands in exo positions predicts symmetric and asymmetric stretches at 1938 and 1909 cm−1 respectively, with relative band intensities of ~3.5:1, in good agreement with experiment. From the observed IR intensities, we find that Hi-3 is present at a concentration about equal to that of the EPR-active Hi-1 species. The relevance of Hi-3 to the nitrogenase catalytic mechanism and its recently discovered Fischer-Tropsch chemistry is discussed. PMID:23136072
NASA Astrophysics Data System (ADS)
Takahashi, Hirona; Hagiwara, Kenta; Kawai, Akio
2016-11-01
Addition reaction of photo-generated radicals to double bonds of diethyl fumarate (deF) and diethyl maleate (deM), which are geometrical isomers, was studied by means of time-resolved- (TR-) and pulsed-electron paramagnetic resonance (EPR). Analysis of TR-EPR spectra indicates that adduct radicals from deF and deM should have the same structure. The double bonds of these monomers are converted to single ones by addition reaction, which allows hindered internal rotation to give the same structure of adduct radical. The rate constants for addition reaction of photo-generated radicals were determined by Stern-Volmer analysis of the decay time of electron spin-echo intensity of these radicals measured by the pulsed EPR method. Rate constants for deF were found to be larger than those for deM. This relation is in good consistent with efficiency of polymerisation of deF and deM. Experimentally determined rate constants were evaluated by introducing the addition reaction model on the basis of two important factors enthalpy and polar effects.
NASA Astrophysics Data System (ADS)
Lenka, Manas K.; Sharma, Amit; Sharma, Jaibir; DasGupta, Amitava
2012-10-01
This paper describes the design and simulation of RF MEMS SPST shunt and SPDT shunt-shunt switches with modified coplanar waveguide (CPW) configuration for X-band and Ku-band applications exhibiting high isolation and low insertion loss. By modifying the basic CPW structure for a six-strip membrane having length 720 μm, the resonant frequency can be reduced from 33.5 GHz to 13.5 GHz with isolation as high as -30 dB(-63 dB at resonant frequency) in Ku-band. Similar results are also found in case SPST and SPDT switches with other membrane types.
Electron paramagnetic resonance (EPR) is a technique for studying chemical species that have one or more unpaired electrons. The current invention describes Echo-based Single Point Imaging (ESPI), a novel EPR image formation strategy that allows in vivo imaging of physiological function. The National Cancer Institute's Radiation Biology Branch is seeking statements of capability or interest from parties interested in in-licensing an in vivo imaging using Electron paramagnetic resonance (EPR) to measure active oxygen species.
NASA Technical Reports Server (NTRS)
Withington, J. R.; Williams, W. F.
1982-01-01
Williams and Withington (1979) have considered a prototype X-S-band feedhorn which enabled simultaneous X- and S-band reception from a Cassegrain antenna. This feedhorn has quite successfully demonstrated an alternate method to the standard Deep Space Network (DSN) system of multiple subreflectors and dichroic plate for dual-band reception. In connection with a Network Consolidation Program, involving centralized control of existing antennas and construction of new reflector antennas, a second-generation feedhorn/combiner was conceived to show that this common-aperture feedhorn system was capable of performing all necessary functions the DSN would be called upon to perform with existing and future X-S-band spacecraft. Attention is given to the feedhorn concept, the combiner concept, the first and the second generation of the horn, Sand X-band tuning, and planned capabilities. The feedhorn greatly extends the state of the art in DSN performance and will enhance DSN capabilities in the future.
NASA Technical Reports Server (NTRS)
Kahler, S.; Krieger, A. S.
1978-01-01
The technique commonly used for the analysis of data from broad-band X-ray imaging systems for plasma diagnostics is the filter ratio method. This requires the use of two or more broad-band filters to derive temperatures and line-of-sight emission integrals or emission measure distributions as a function of temperature. Here an alternative analytical approach is proposed in which the temperature response of the imaging system is matched to the physical parameter being investigated. The temperature response of a system designed to measure the total radiated power along the line of sight of any coronal structure is calculated. Other examples are discussed.
NASA Astrophysics Data System (ADS)
Landmann, M.; Rauls, E.; Schmidt, W. G.
2017-04-01
The composition dependence of the natural band alignment at nonpolar AlxGa1 -xN /AlyGa1 -yN heterojunctions is investigated via hybrid functional based density functional theory. Accurate band-gap data are provided using Heyd-Scuseria-Ernzerhof (HSE) type hybrid functionals with a composition dependent exact-exchange contribution. The unstrained band alignment between zincblende (zb) AlxGa1 -xN semiconductor alloys is studied within the entire ternary composition range utilizing the Branch-point technique to align the energy levels related to the bulklike direct Γv→Γc and indirect, pseudodirect, respectively, Γv→Xc type transitions in zb-AlxGa1 -xN . While the zb-GaN/AlxGa1 -xN band edges consistently show a type-I alignment, the relative position of fundamental band edges changes to a type-II alignment in the Al-rich composition ranges of zb-AlxGa1 -xN /AlN and zb-AlxGa1 -xN /AlyGa1 -yN systems. The presence of a direct-indirect band-gap transition at xc=0.63 in zb-AlxGa1 -xN semiconductor alloys gives rise to a notably different composition dependence of band discontinuities in the direct and indirect energy-gap ranges. Below the critical direct-indirect Al/Ga-crossover concentration, the band offsets show a close to linear dependence on the alloy composition. In contrast, notable bowing characteristics of all band discontinuities are observed above the critical crossover composition.
Islam, M. T.; Samsuzzaman, M.
2014-01-01
This paper introduces a new configuration of compact, triangular- and diamond-slotted, microstrip-fed, low-profile antenna for C/X band applications on polytetrafluoroethylene glass microfiber reinforced material substrate. The antenna is composed of a rectangular-shaped patch containing eight triangles and two diamond-shaped slots and an elliptical-slotted ground plane. The rectangular-shaped patch is obtained by cutting two diamond slots in the middle of the rectangular patch, six triangular slots on the left and right side of the patch, and two triangular slots on the up and down side of the patch. The slotted radiating patch, the elliptical-slotted ground plane, and the microstrip feed enable the matching bandwidth to be widened. A prototype of the optimized antenna was fabricated on polytetrafluoroethylene glass microfiber reinforced material substrate using LPKF prototyping machine and investigated to validate the proposed design. The simulated results are compared with the measured data, and good agreement is achieved. The proposed antenna offers fractional bandwidths of 13.69% (7.78–8.91 GHz) and 10.35% (9.16–10.19 GHz) where S11 < −10 dB at center frequencies of 8.25 GHz and 9.95 GHz, respectively, and relatively stable gain, good radiation efficiency, and omnidirectional radiation patterns in the matching band. PMID:24987742
VO2+ ions in zinc lead borate glasses studied by EPR and optical absorption techniques.
Prakash, P Giri; Rao, J Lakshmana
2005-09-01
Electron paramagnetic resonance (EPR) and optical absorption spectra of vanadyl ions in zinc lead borate (ZnO-PbO-B2O3) glass system have been studied. EPR spectra of all the glass samples exhibit resonance signals characteristic of VO2+ ions. The values of spin-Hamiltonian parameters indicate that the VO2+ ions in zinc lead borate glasses were present in octahedral sites with tetragonal compression and belong to C4V symmetry. The spin-Hamiltonian parameters g and A are found to be independent of V2O5 content and temperature but changing with ZnO content. The decrease in Deltag( parallel)/Deltag( perpendicular) value with increase in ZnO content indicates that the symmetry around VO2+ ions is more octahedral. The decrease in intensity of EPR signal above 10 mol% of V2O5 is attributed to a fall in the ratio of the number of V4+ ions (N4) to the number of V5+ ions (N5). The number of spins (N) participating in resonance was calculated as a function of temperature for VO2+ doped zinc lead borate glass sample and the activation energy was calculated. From the EPR data, the paramagnetic susceptibility was calculated at various temperatures and the Curie constant was evaluated from the 1/chi-T graph. The optical absorption spectra show single absorption band due to VO2+ ions in tetragonally distorted octahedral sites.
The view from the trenches: part 2-technical considerations for EPR screening.
Nicolalde, Roberto J; Gougelet, Robert M; Rea, Michael; Williams, Benjamin B; Dong, Ruhong; Kmiec, Maciej M; Lesniewski, Piotr N; Swartz, Harold M
2010-02-01
There is growing awareness of the need for methodologies that can be used retrospectively to provide the biodosimetry needed to carry out screening and triage immediately after an event in which large numbers of people have potentially received clinically significant doses of ionizing radiation. The general approach to developing such methodologies has been a technology centric one, often ignoring the system integrations considerations that are key to their effective use. In this study an integrative approach for the evaluation and development of a physical biodosimetry technology was applied based on in vivo electron paramagnetic resonance (EPR) dosimetry. The EPR measurements are based on physical changes in tissues whose magnitudes are not affected by the factors that can confound biologically-based assessments. In this study the use of a pilot simulation exercise to evaluate an experimental EPR system and gather stakeholders' feedback early on in the development process is described. The exercise involved: ten non-irradiated participants, representatives from a local fire department; Department of Homeland Security certified exercise evaluators, EPR experts, physicians; and a human factors engineer. Stakeholders were in agreement that the EPR technology in its current state of development could be deployed for the screening of mass casualties. Furthermore, stakeholders' recommendations will be prioritized and incorporated in future developments of the EPR technique. While the results of this exercise were aimed specifically at providing feedback for the development of EPR dosimetry for screening mass casualties, the methods and lessons learned are likely to be applicable to other biodosimetric methods.
EPR Steering inequalities with Communication Assistance
Nagy, Sándor; Vértesi, Tamás
2016-01-01
In this paper, we investigate the communication cost of reproducing Einstein-Podolsky-Rosen (EPR) steering correlations arising from bipartite quantum systems. We characterize the set of bipartite quantum states which admits a local hidden state model augmented with c bits of classical communication from an untrusted party (Alice) to a trusted party (Bob). In case of one bit of information (c = 1), we show that this set has a nontrivial intersection with the sets admitting a local hidden state and a local hidden variables model for projective measurements. On the other hand, we find that an infinite amount of classical communication is required from an untrusted Alice to a trusted Bob to simulate the EPR steering correlations produced by a two-qubit maximally entangled state. It is conjectured that a state-of-the-art quantum experiment would be able to falsify two bits of communication this way. PMID:26880376
High Power SiGe X-Band (8-10 GHz) Heterojunction Bipolar Transistors and Amplifiers
NASA Technical Reports Server (NTRS)
Ma, Zhenqiang; Jiang, Ningyue; Ponchak, George E.; Alterovitz, Samuel A.
2005-01-01
Limited by increased parasitics and thermal effects as the device size becomes large, current commercial SiGe power HBTs are difficult to operate at X-band (8-12 GHz) with adequate power added efficiencies at high power levels. We found that, by changing the heterostructure and doping profile of SiGe HBTs, their power gain can be significantly improved without resorting to substantial lateral scaling. Furthermore, employing a common-base configuration with proper doping profile instead of a common-emitter configuration improves the power gain characteristics of SiGe HBTs, which thus permits these devices to be efficiently operated at X-band. In this paper, we report the results of SiGe power HBTs and MMIC power amplifiers operating at 8-10 GHz. At 10 GHz, 22.5 dBm (178 mW) RF output power with concurrent gain of 7.32 dB is measured at the peak power-added efficiency of 20.0% and the maximum RF output power of 24.0 dBm (250 mW) is achieved from a 20 emitter finger SiGe power HBT. Demonstration of single-stage X-band medium-power linear MMIC power amplifier is also realized at 8 GHz. Employing a 10-emitter finger SiGe HBT and on-chip input and output matching passive components, a linear gain of 9.7 dB, a maximum output power of 23.4 dBm and peak power added efficiency of 16% is achieved from the power amplifier. The MMIC exhibits very low distortion with third order intermodulation (IM) suppression C/I of -13 dBc at output power of 21.2 dBm and over 20dBm third order output intercept point (OIP3).
NASA Astrophysics Data System (ADS)
Yordanov, Nicola D.; Aleksieva, Katerina
2009-03-01
The results of electron paramagnetic resonance (EPR) study on fresh fruits (whole pulp of pears, apples, peaches, apricots, avocado, kiwi and mango) before and after gamma-irradiation are reported using two drying procedures before EPR investigation. In order to remove water from non-irradiated and irradiated samples of the first batch, the pulp of fresh fruits is pressed, and the solid residue is washed with alcohol and dried at room temperature. The fruits of the second batch are pressed and dried in a standard laboratory oven at 40 °C. The results obtained with both drying procedures are compared. All samples under study show a singlet EPR line with g=2.0048±0.0005 before irradiation. Irradiation gives rise to typical "cellulose-like" EPR spectrum featuring one intensive line with g=2.0048±0.0005 and two very weak satellite lines situated 3 mT at left and right of the central line. Only mango samples show a singlet line after irradiation. The fading kinetics of radiation-induced EPR signal is studied for a period of 50 days after irradiation. When the irradiated fruit samples are stored in their natural state and dried just before each EPR measurement, the satellite lines are measurable for less than 17 days of storage. Irradiated fruit samples, when stored dried, lose for 50 days ca. 40% of their radiation-induced radicals if treated with alcohol or ca. 70% if dried in an oven. The reported results unambiguously show that the presence of the satellite lines in the EPR spectra could be used for identification of radiation processing of fresh fruits, thus extending the validity of European Protocol EN 1787 (2000). Foodstuffs—Detection of Irradiated Food Containing Cellulose by EPR Spectroscopy. European Committee for Standardisation. Brussels for dry herbs.
NASA Astrophysics Data System (ADS)
Shim, Kyurhee
2013-11-01
A theoretical model utilizing a universal tight binding method and a correlated function expansion technique is presented to calculate the valence band maximum (VBM) and the conduction band minimum (CBM) of the binary (GaAs, InAS, GaSb, and InSb) and quaternary alloy GaxIn1-xAsySb1-y systems. By organizing the relative positions of the VBM and CBM between semiconductors, the band alignments and band types in the heterojunctions are determined. A straddling (type-I) band alignment in InAs/GaAs, InSb/GaAs, and GaSb/InSb, staggered (type-II) band alignment in GaSb/GaAs, and broken (type-III) band alignment in InSb/InAs and InAs/GaSb are found respectively. In addition, the compositional variations of VBM, CBM, valence band offset, conduction band offset, and band type for the alloy GaxIn1-xAsySb1-y lattice matched on GaSb and InAs are obtained as increasing the composition x. A pronounced upward bowing for the VBM and a very slight upward bowing (almost linear) for CBM are found, respectively. By controlling the compositions (x, y), band type transitions occur. The GaxIn1-xAsySb1-y heterojunctions lattice matched to GaSb changes their band types from type-III at x ˜0→ to type-II at x = 0.07, and → to type-I at x = 0.38. In contrast, the GaxIn1-xAsySb1-y heterojunctions lattice matched to InAs changes their band types from type-II x ˜0→ to type-III at x = 0.32. Reasonable agreement is obtained between our theoretical results and existing experimental data.
Measurements of the ClO radical vibrational band intensity and the ClO + ClO + M reaction product
NASA Technical Reports Server (NTRS)
Burkholder, James B.; Orlando, John J.; Hammer, Philip D.; Howard, Carleton J.; Goldman, Aaron
1988-01-01
There is considerable interest in the kinetics and concentrations of free radicals in the stratosphere. Chlorine monoxide is a critically important radical because of its role in catalytic cycles for ozone depletion. Depletion occurs under a wide variety of conditions including the Antarctic spring when unusual mechanisms such as the BrO sub x/ClO sub x, ClO dimer (Cl sub 2 O sub 2), and ClO sub x/HO sub x cycles are suggested to operate. Infrared spectroscopy is one of the methods used to measure ClO in the stratosphere (Menzies 1979 and 1983; Mumma et al., 1983). To aid the quantification of such infrared measurements, researchers measured the ClO ground state fundamental band intensity.
On the Correlations between the Particles in the EPR-Paradoxon
NASA Astrophysics Data System (ADS)
Treder, H.-J.
The Einstein-Podolsky-Rosen gedanken-experiment does not imply non-local interactions or an action-at-a-distance.Contrary, the EPR proves the measurements at one particle does not have influences at canonical variables of the other particles if the quantum-mechanical commutation relations are true.But, the EPR implices correlations between the particles which come in by subjective knowledge. These correlations are a priori informations about the relative motion or, complementarily, about the motion of the center of mass. The impression of an action-at-a-distance is produced by the use of usual particle coordinates in the EPR-arrangements.The discussion of the Einstein-Podolsky-Rosen gedanken-experiment (EPR) has been going on over fifty years. EINSTEIN, PODOLSKY, and ROSEN formulated their famous paradox in 1935, and in the discussion between N. BOHR (1935, 1949) and A. EINSTEIN (1936, 1948); A. EINSTEIN (1948) made his point that the EPR implied an action-at-a-distance for quantum-mechanical particles (without obvious classical interactions). His argument is the starting point for the recent discussion about EPR and causality (see A. Aspect, 1981).Translated Abstract
NASA Astrophysics Data System (ADS)
Pons, A.; David, C.; Fortin, J.; Stanchits, S.; MenéNdez, B.; Mengus, J. M.
2011-03-01
To investigate the effect of compaction bands (CB) on fluid flow, capillary imbibition experiments were performed on Bentheim sandstone specimens (initial porosity ˜22.7%) using an industrial X-ray scanner. We used a three-step procedure combining (1) X-ray imaging of capillary rise in intact Bentheim sandstone, (2) formation of compaction band under triaxial tests, at 185 MPa effective pressure, with acoustic emissions (AE) recording for localization of the induced damage, and (3) again X-ray imaging of capillary rise in the damaged specimens after the unloading. The experiments were performed on intact cylindrical specimens, 5 cm in diameter and 10.5 cm in length, cored in different orientations (parallel or perpendicular to the bedding). Analysis of the images obtained at different stages of the capillary imbibition shows that the presence of CB slows down the imbibition and disturbs the geometry of water flow. In addition, we show that the CB geometry derived from X-ray density maps analysis is well correlated with the AE location obtained during triaxial test. The analysis of the water front kinetics was conducted using a simple theoretical model, which allowed us to confirm that compaction bands act as a barrier for fluid flow, not fully impermeable though. We estimate a contrast of permeability of a factor of ˜3 between the host rock and the compaction bands. This estimation of the permeability inside the compaction band is consistent with estimations done in similar sandstones from field studies but differs by 1 order of magnitude from estimations from previous laboratory measurements.
Passive Microwave Measurements Over Conifer Forests at L-Band and C-Band
NASA Technical Reports Server (NTRS)
LeVine, D. M.; Lang, R.; Chauhan, N.; Kim, E.; Bidwell, S.; Goodberlet, M.; Haken, M.; deMatthaeis, P.
2000-01-01
Measurements have been made at L-band and C-band over conifer forests in Virginia to study the response of passive microwave instruments to biomass and soil moisture. A series of aircraft measurements were made in July, August and November, 1999 over relatively homogenous conifer forests of varying biomass. Three radiometers participated in these measurements. These were: 1) the L-band radiometer ESTAR, a horizontally polarized synthetic aperture radiometer which has been used extensively in past measurements of soil moisture; 2) the L-band radiometer SLFMR, a vertically polarized cross-track scanner which has been used successfully in the past for mapping sea surface salinity; and 3) The ACMR, a new C-band radiometer which operates at V- and H-polarization and in the configuration for these experiments did not scan. All three radiometers were flown on the NASA P-3 aircraft based at the Goddard Space Flight Center's Wallops Flight Facility. The ESTAR and SLFMR were mounted in the bomb bay of the P-3 and imaged across track whereas the ACMR was mounted to look aft at 54 degrees up from nadir. Data was collected at altitudes of 915 meters and 457 meters. The forests consisted of relatively homogeneous "managed" stands of conifer located near Waverly, Virginia. This is a relatively flat area about 30 miles southeast of Richmond, VA with numerous stands of trees being grown for the forestry industry. The stands selected for study consisted of areas of regrowth and mature stands of pine. In addition, a small stand of very large trees was observed. Soil moisture sampling was done in each stand during the aircraft over flights. Data was collected on July 7, August 27, November 15 and November 30, 1999. Measurements were made with ESTAR on all days. The ACMR flew on the summer missions and the SLFMR was present only on the August 27 flight. Soil moisture varied from quite dry on July 7 to quite moist on November 30 (which was shortly after a period of rain). The microwave
NASA Astrophysics Data System (ADS)
Yadav, Arti; Khasa, Satish; Hooda, Ashima; Dahiya, Manjeet S.; Agarwal, Ashish; Chand, Prem
2016-03-01
Glasses having composition 7NiO • 23Li2O • 20Bi2O3 • 50B2O3, 7V2O5 • 23Li2O • 20Bi2O3 • 50B2O3 and x(2NiO • V2O5) • (30 - x)Li2O • 50B2O3 • 20Bi2O3 (with x = 0, 2, 5, 7 & 10 mol%) prepared through melt-quench route are explored by analyzing density, impedance spectroscopy and electron paramagnetic resonance (EPR). It is found that both density and molar volume increase with an increase in substitution of 2NiO • V2O5 in the base glass matrix. Different dielectric parameters viz. dielectric loss (ε), electrical modulus (M), loss tangent (tanδ) etc. are evaluated and their variations with frequency and temperature are analyzed which reveals that these glasses exhibit a non-Debye relaxation behavior. A phenomenal description of the capacitive behavior is obtained by considering the circuitry as a parallel combination of bulk resistance (Rb) and constant phase element (CPE). The conduction mechanism is found to follow Quantum Mechanical Tunneling (QMT) model. Spin Hamiltonian Parameters (SHPs) and covalency rates are calculated from the EPR spectra of vanadyl ion. The observed EPR spectra confirmed that V4 + ion exists as vanadyl ion in the octahedral coordination with tetragonal compression.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Kumar, Vipin, E-mail: vipinkumar28@yahoo.co.in; Sharma, D. K.; Agrawal, Sonalika
Cd{sub 1-X}Zn{sub X}S thin films (X = 0.2, 0.4, 0.6, 0.8) have been grown on glass substrate by spray pyrolysis technique using equimolar concentration aqueous solution of cadmium chloride, zinc acetate and thiourea. Prepared thin films have been characterized by UV-VIS spectrophotometer. The optical band gap of the films has been studied by transmission spectra in wavelength range 325-600nm. It has been observed that optical band gap increases with increasing zinc concentration. The optical band gap of these thin films varies from 2.59 to 3.20eV with increasing Zn content.
Identification of gamma-irradiated fruit juices by EPR spectroscopy
NASA Astrophysics Data System (ADS)
Aleksieva, K. I.; Dimov, K. G.; Yordanov, N. D.
2014-10-01
The results of electron paramagnetic resonance (EPR) study on commercially available juices from various fruits and different fruit contents: 25%, 40%, 50%, and 100%, homemade juices, nectars and concentrated fruit syrups, before and after gamma-irradiation are reported. In order to remove water from non- and irradiated samples all juices and nectars were filtered; the solid residue was washed with alcohol and dried at room temperature. Only concentrated fruit syrups were dried for 60 min at 40 °C in a standard laboratory oven. All samples under study show a singlet EPR line with g=2.0025 before irradiation with exception of concentrated fruit syrups, which are EPR silent. Irradiation of juice samples gives rise to complex EPR spectra which gradually transferred to "cellulose-like" EPR spectrum from 25% to 100% fruit content. Concentrated fruit syrups show typical "sugar-like" spectra due to added saccharides. All EPR spectra are characteristic and can prove radiation treatment. The fading kinetics of radiation-induced EPR signals were studied for a period of 60 days after irradiation.
Accurate determination of the valence band edge in hard x-ray photoemission spectra using GW theory
DOE Office of Scientific and Technical Information (OSTI.GOV)
Lischner, Johannes, E-mail: jlischner597@gmail.com; Department of Physics and Department of Materials and the Thomas Young Centre for Theory and Simulation of Materials, Imperial College London, London SW7 2AZ; Nemšák, Slavomír
We introduce a new method for determining accurate values of the valence-band maximum in x-ray photoemission spectra. Specifically, we align the sharpest peak in the valence-band region of the experimental spectrum with the corresponding feature of a theoretical valence-band density of states curve from ab initio GW theory calculations. This method is particularly useful for soft and hard x-ray photoemission studies of materials with a mixture of valence-band characters, where strong matrix element effects can render standard methods for extracting the valence-band maximum unreliable. We apply our method to hydrogen-terminated boron-doped diamond, which is a promising substrate material for novelmore » solar cell devices. By carrying out photoemission experiments with variable light polarizations, we verify the accuracy of our analysis and the general validity of the method.« less
On Orbit Measurement of Response vs. Scan Angle for the Infrared Bands on TRMM/VIRS
NASA Technical Reports Server (NTRS)
Barnes, William L.; Lyu, Cheng-Hsuan; Barnes, Robert A.
1999-01-01
The Visible and Infrared Scanner on the Tropical Rainfall Measuring Mission (TRMM/VIRS) is a whiskbroom imaging radiometer with two reflected solar bands and three emissive infrared bands. All five detectors are on a single cooled focal plane. This configuration necessitated the use of a paddlewheel scan mirror to avoid the effects of focal plane rotation that arise when using a scan mirror that is inclined to its axis of rotation. System radiometric requirements led to the need for protected silver as the mirror surface. Unfortunately, the SiO(x) coatings currently used to protect silver from oxidation introduce a change in reflectance with angle of incidence (AOI). This AOI dependence results in a modulation of system level response with scan angle. Measurement of system response vs. scan angle (RVS) was not difficult for the VIRS reflected solar bands, but attaining the required accuracy for the IR bands in the laboratory was not possible without a large vacuum chamber and a considerable amount of custom designed testing apparatus. Therefore, the decision was made to conduct the measurement on-orbit. On three separate occasions, the TRMM spacecraft was rotated about its pitch axis and, after the nadir view passed over the Earth's limb, the VIRS performed several thousand scans while viewing deep space. The resulting data has been analyzed and the RVS curves generated for the three IR bands are being used in the VIRS radiometric calibration algorithm. This, to our knowledge, the first time this measurement has been made on-orbit. Similar measurements are planned for the EOS-AM and EOS-PM MODIS sensors and are being considered for several systems under development. The VIRS on-orbit results will be compared to VIRS and MODIS system level laboratory measurements, MODIS scan mirror witness sample measurements and modeled data.
NASA Astrophysics Data System (ADS)
Bahrenberg, Thorsten; Rosenski, Yael; Carmieli, Raanan; Zibzener, Koby; Qi, Mian; Frydman, Veronica; Godt, Adelheid; Goldfarb, Daniella; Feintuch, Akiva
2017-10-01
Chirp and shaped pulses have been recently shown to be highly advantageous for improving sensitivity in DEER (double electron-electron resonance, also called PELDOR) measurements due to their large excitation bandwidth. The implementation of such pulses for pulse EPR has become feasible due to the availability of arbitrary waveform generators (AWG) with high sampling rates to support pulse shaping for pulses with tens of nanoseconds duration. Here we present a setup for obtaining chirp pulses on our home-built W-band (95 GHz) spectrometer and demonstrate its performance on Gd(III)-Gd(III) and nitroxide-nitroxide DEER measurements. We carried out an extensive optimization procedure on two model systems, Gd(III)-PyMTA-spacer-Gd(III)-PyMTA (Gd-PyMTA ruler; zero-field splitting parameter (ZFS) D ∼ 1150 MHz) as well as nitroxide-spacer-nitroxide (nitroxide ruler) to evaluate the applicability of shaped pulses to Gd(III) complexes and nitroxides, which are two important classes of spin labels used in modern DEER/EPR experiments. We applied our findings to ubiquitin, doubly labeled with Gd-DOTA-monoamide (D ∼ 550 MHz) as a model for a system with a small ZFS. Our experiments were focused on the questions (i) what are the best conditions for positioning of the detection frequency, (ii) which pump pulse parameters (bandwidth, positioning in the spectrum, length) yield the best signal-to-noise ratio (SNR) improvements when compared to classical DEER, and (iii) how do the sample's spectral parameters influence the experiment. For the nitroxide ruler, we report an improvement of up to 1.9 in total SNR, while for the Gd-PyMTA ruler the improvement was 3.1-3.4 and for Gd-DOTA-monoamide labeled ubiquitin it was a factor of 1.8. Whereas for the Gd-PyMTA ruler the two setups pump on maximum and observe on maximum gave about the same improvement, for Gd-DOTA-monoamide a significant difference was found. In general the choice of the best set of parameters depends on the D
Development for a supercompact X -band pulse compression system and its application at SLAC
Wang, Juwen W.; Tantawi, Sami G.; Xu, Chen; ...
2017-11-09
Here, we have successfully designed, fabricated, installed, and tested a super compact X -band SLAC Energy Doubler system at SLAC. It is composed of an elegant 3 dB coupler–mode converter–polarizer coupled to a single spherical energy storage cavity with high Q 0 of 94000 and a diameter less than 12 cm. The available rf peak power of 50 MW can be compressed to a peak average power of more than 200 MW in order to double the kick for the electron bunches in a rf transverse deflector system and greatly improve the measurement resolution of both the electron bunches andmore » the x-ray free-electron laser pulses. The design physics and fabrication as well as the measurement results will be presented in detail. High-power operation has demonstrated the excellent performance of this rf compression system without rf breakdown, sign of pulse heating, and rf radiation.« less
Development for a supercompact X -band pulse compression system and its application at SLAC
DOE Office of Scientific and Technical Information (OSTI.GOV)
Wang, Juwen W.; Tantawi, Sami G.; Xu, Chen
Here, we have successfully designed, fabricated, installed, and tested a super compact X -band SLAC Energy Doubler system at SLAC. It is composed of an elegant 3 dB coupler–mode converter–polarizer coupled to a single spherical energy storage cavity with high Q 0 of 94000 and a diameter less than 12 cm. The available rf peak power of 50 MW can be compressed to a peak average power of more than 200 MW in order to double the kick for the electron bunches in a rf transverse deflector system and greatly improve the measurement resolution of both the electron bunches andmore » the x-ray free-electron laser pulses. The design physics and fabrication as well as the measurement results will be presented in detail. High-power operation has demonstrated the excellent performance of this rf compression system without rf breakdown, sign of pulse heating, and rf radiation.« less
Khan, Nadeem; Mupparaju, Sriram; Hou, Huagang; Williams, Benjamin B.; Swartz, Harold
2011-01-01
Tumor hypoxia plays a vital role in therapeutic resistance. Consequently, measurements of tumor pO2 could be used to optimize the outcome of oxygen-dependent therapies, such as, chemoradiation. However, the potential optimizations are restricted by the lack of methods to repeatedly and quantitatively assess tumor pO2 during therapies, particularly in gliomas. We describe the procedures for repeated measurements of orthotopic glioma pO2 by multi-site electron paramagnetic resonance (EPR) oximetry. This oximetry approach provides simultaneous measurements of pO2 at more than one site in the glioma and contralateral cerebral tissue. The pO2 of intracerebral 9L, C6, F98 and U251 tumors, as well as contralateral brain, were measured repeatedly for five consecutive days. The 9L glioma was well oxygenated with pO2 of 27 - 36 mm Hg, while C6, F98 and U251 glioma were hypoxic with pO2 of 7 - 12 mm Hg. The potential of multi-site EPR oximetry to assess temporal changes in tissue pO2 was investigated in rats breathing 100% O2. A significant increase in F98 tumor and contralateral brain pO2 was observed on day 1 and day 2, however, glioma oxygenation declined on subsequent days. In conclusion, EPR oximetry provides the capability to repeatedly assess temporal changes in orthotopic glioma pO2. This information could be used to test and optimize the methods being developed to modulate tumor hypoxia. Furthermore, EPR oximetry could be potentially used to enhance the outcome of chemoradiation by scheduling treatments at times of increase in glioma pO2. PMID:22079559
NASA Technical Reports Server (NTRS)
Mysoor, Narayan R.; Mueller, Robert O.
1991-01-01
This paper summarizes the design concepts, analyses, and the development of an X-band transponder low-loss linear phase modulator for deep space spacecraft applications. A single section breadboard circulator-coupled reflection phase modulator has been analyzed, fabricated, and evaluated. Two- and three-cascaded sections have been modeled and simulations performed to provide an X-band DST phase modulator with +/- 2.5 radians of peak phase deviation to accommodate down-link signal modulation with composite telemetry data and ranging with a deviation linearity tolerance +/- 8 percent and insertion loss of less than 10 +/- 0.5 dB. A two-section phase modulator using constant gamma hyperabrupt varactors and an efficient modulator driver circuit was breadboarded. The measured results satisfy the DST phase modulator requirements, and excellent agreement with the predicted results.
Solid-State Powered X-band Accelerator
DOE Office of Scientific and Technical Information (OSTI.GOV)
Othman, Mohamed A.K.; Nann, Emilio A.; Dolgashev, Valery A.
2017-03-06
In this report we disseminate the hot test results of an X-band 100-W solid state amplifier chain for linear accelerator (linac) applications. Solid state power amplifiers have become increasingly attractive solutions for achieving high power in radar and maritime applications. Here the performance of solid state amplifiers when driving an RF cavity is investigated. Commercially available, matched and fully-packaged GaN on SiC HEMTs are utilized, comprising a wideband driver stage and two power stages. The amplifier chain has a high poweradded- efficiency and is able to supply up to ~1.2 MV/m field gradient at 9.2 GHz in a simple testmore » cavity, with a peak power exceeding 100 W. These findings set forth the enabling technology for solid-state powered linacs.« less
EPR spectral investigation of radiation-induced radicals of gallic acid.
Tuner, Hasan
2017-11-01
In the present work, spectroscopic features of the radiation-induced radicals of gallic acid compounds were investigated using electron paramagnetic resonance (EPR) spectroscopy. While un-irradiated samples presented no EPR signal, irradiated samples exhibited an EPR spectrum consisting of an intense resonance line at the center and weak lines on both sides. Detailed microwave saturation investigations were carried out to determine the origin of the experimental EPR lines. It is concluded that the two side lines of the triplet satellite originate from forbidden "spin-flip" transitions. The spectroscopic and structural features of the radiation-induced radicals were determined using EPR spectrum fittings. The experimental EPR spectra of the two gallic acid compounds were consistent with the calculated EPR spectroscopic features of the proposed radicals. It is concluded that the most probable radicals are the cyclohexadienyl-type, [Formula: see text] radicals for both compounds.
Einstein coefficients for rotational lines of the (0,0) band of the NO A2sigma(+)-X2Pi system
NASA Technical Reports Server (NTRS)
Reisel, John R.; Carter, Campbell D.; Laurendeau, Normand M.
1992-01-01
A summary of the spectroscopic equations necessary for prediction of the molecular transition energies and the Einstein A and B coefficients for rovibronic lines of the gamma(0,0) band of nitric oxide (NO) is presented. The calculated molecular transition energies are all within 0.57/cm of published experimental values; in addition, over 95 percent of the calculated energies give agreement with measured results within 0.25/cm. Einstein coefficients are calculated from the band A00 value and the known Hoenl-London factors and are tabulated for individual rovibronic transitions in the NO A2sigma(+)-X2Pi(0,0) band.
NASA Astrophysics Data System (ADS)
Tang, Lanqin; Kuai, Libang; Li, Yichang; Li, Haijin; Zhou, Yong; Zou, Zhigang
2018-02-01
A series of Zn x Cd1-x S monodispersed nanospheres were successfully synthesized with tunable band structures. As-prepared Zn x Cd1-x S solid solutions show much enhanced photocatalytic efficiency for CO2 photoreduction in aqueous solutions under visible light irradiation, relative to pure CdS analog. Methanol (CH3OH) and acetaldehyde (CH3CHO) are the major products of CO2 photoreduction for the solid solutions with x = 0, 0.2, and 0.5. Interestingly, Zn0.8Cd0.2S photocatalyst with a wide band gap can also additionally generate ethanol (CH3CH2OH) besides CH3OH and CH3CHO. The balance between the band structure-directing redox capacity and light absorption should be considered to influence both product yield and selectivity of CO2 photoreduction. The possible photoreduction mechanism was tentatively proposed.
Band bending at magnetic Ni/Ge(001) interface investigated by X-ray photoelectron spectroscopy
NASA Astrophysics Data System (ADS)
Bocîrnea, Amelia Elena; Tănase, Liviu Cristian; Costescu, Ruxandra Maria; Apostol, Nicoleta Georgiana; Teodorescu, Cristian Mihail
2017-12-01
We report the molecular beam epitaxy growth of Ni on a clean Ge(001) surface with an intermediate NiGe layer forming at the interface at room temperature. The crystallinity of the substrate is lost after the deposition of more than 2 Ni monolayers. The Schottky barrier formation is investigated by X-ray photoelectron spectroscopy. The method allows us to infer a 0.39-0.45 eV band bending at the interface between the compound and Ge(001). Magneto-optical Kerr effect measurements were conclusive in detecting the ferromagnetic ordering of Ni outermost layers.
Electron temperature from x-ray continuum measurements on the NIF
NASA Astrophysics Data System (ADS)
Jarrott, Leonard; Bachmann, Benjamin; Benedetti, Robin; Izumi, Nobuhiko; Khan, Shahab; Landen, Otto; Ma, Tammy; Nagel, Sabrina; Pak, Arthur; Patel, Prav; Schneider, Marilyn; Springer, Paul; LLNL Collaboration
2017-10-01
We report on measurements of the electron temperature within the hot spot of inertially confined, layered implosions on the NIF using a titanium differential filtering x-ray diagnostic. The electron temperature from x-ray emission is insensitive to non-thermal velocity flows as is the case with ion temperature measurements and is thus a critical parameter in interpreting stagnated hot spot conditions. Here we discuss measurements using titanium filters ranging from 10 μm to 1mm in thickness with a sensitivity band of 10-30keV coupled with penumbral pinholes. The use of larger pinhole diameters increases x-ray fluence improving sensitivity of photon energies with minimal attenuation from the compressed fuel/shell. This diagnostic has been fielded on a series of cryogenic shots with DT ion temperatures ranging from 2-5keV. Analysis of the measurement will be presented along with a comparison against simulated electron temperatures and x-ray spectra as well as a comparison to DT ion temperature measurements. This work was performed under the auspices of U.S. DoE by LLNL under Contract No. DE-AC52-07NA27344.
Upender, G; Babu, J Chinna; Mouli, V Chandra
2012-04-01
X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), energy dispersive X-ray spectrometry (EDS), differential scanning calorimetry (DSC), infrared (IR), Raman, electron paramagnetic resonance (EPR) and optical absorption studies on 10Li2O-xP2O5-(89-x)TeO2-1CuO glasses (where x=5, 10, 15, 20 and 25 mol%) have been carried out. The amorphous nature of the glasses was confirmed using XRD and FESEM measurements. The glass transition temperature (Tg) of glass samples have been estimated from DSC traces and found that the Tg increases with increasing P2O5 content. Both the IR and Raman studies have been showed that the present glass system consists of [TeO3], [TeO4], [PO3] and [PO4] units. The spin-Hamiltonian parameters such as g∥, g⊥, and A∥ have been determined from EPR spectra and it was found that the Cu2+ ion is present in tetragonal distorted octahedral site with [Formula: see text] as the ground state. Bonding parameters and bonding symmetry of Cu2+ ions have been calculated by correlating EPR and optical data and were found to be composition dependent. Copyright © 2012 Elsevier B.V. All rights reserved.
Characterization of Mediterranean hail-bearing storms using an operational polarimetric X-band radar
NASA Astrophysics Data System (ADS)
Vulpiani, G.; Baldini, L.; Roberto, N.
2015-11-01
This work documents the effective use of X-band radar observations for monitoring severe storms in an operational framework. Two severe hail-bearing Mediterranean storms that occurred in 2013 in southern Italy, flooding two important Sicilian cities, are described in terms of their polarimetric radar signatures and retrieved rainfall fields. The X-band dual-polarization radar operating inside the Catania airport (Sicily, Italy), managed by the Italian Department of Civil Protection, is considered here. A suitable processing is applied to X-band radar measurements. The crucial procedural step relies on the differential phase processing, being preparatory for attenuation correction and rainfall estimation. It is based on an iterative approach that uses a very short-length (1 km) moving window, allowing proper capture of the observed high radial gradients of the differential phase. The parameterization of the attenuation correction algorithm, which uses the reconstructed differential phase shift, is derived from electromagnetic simulations based on 3 years of drop size distribution (DSD) observations collected in Rome (Italy). A fuzzy logic hydrometeor classification algorithm was also adopted to support the analysis of the storm characteristics. The precipitation field amounts were reconstructed using a combined polarimetric rainfall algorithm based on reflectivity and specific differential phase. The first storm was observed on 21 February when a winter convective system that originated in the Tyrrhenian Sea, marginally hit the central-eastern coastline of Sicily, causing a flash flood in Catania. Due to an optimal location (the system is located a few kilometers from the city center), it was possible to retrieve the storm characteristics fairly well, including the amount of rainfall field at the ground. Extemporaneous signal extinction, caused by close-range hail core causing significant differential phase shift in a very short-range path, is documented. The second
Initial Testing of the Mark-0 X-Band RF Gun at SLAC
DOE Office of Scientific and Technical Information (OSTI.GOV)
Vlieks, Arnold; Adolphsen, C.; Dolgashev, V.
A new X-band RF gun (Mark-0) has been assembled, tuned and was tested in the ASTA facility at SLAC. This gun has been improved from an earlier gun used in Compton-scattering experiments at SLAC by the introduction of a racetrack dual-input coupler to reduce quadrupole fields. Waveguide-to-coupler irises were also redesigned to reduce surface magnetic fields and therefore peak pulse surface heating. Tests of this photocathode gun will allow us to gain early operational experience for beam tests of a new gun with further improvements (Mark-1) being prepared for SLAC's X-Band Test Area (XTA) program and the LLNL MEGa-ray program.more » Results of current testing up to {approx} 200 MV/m peak surface Electric fields are presented.« less
Analysis and machine mapping of the distribution of band recoveries
Cowardin, L.M.
1977-01-01
A method of calculating distance and bearing from banding site to recovery location based on the solution of a spherical triangle is presented. X and Y distances on an ordinate grid were applied to computer plotting of recoveries on a map. The advantages and disadvantages of tables of recoveries by State or degree block, axial lines, and distance of recovery from banding site for presentation and comparison of the spatial distribution of band recoveries are discussed. A special web-shaped partition formed by concentric circles about the point of banding and great circles at 30-degree intervals through the point of banding has certain advantages over other methods. Comparison of distributions by means of a X? contingency test is illustrated. The statistic V = X?/N can be used as a measure of difference between two distributions of band recoveries and its possible use is illustrated as a measure of the degree of migrational homing.
Stark Interference of Electric and Magnetic Dipole Transitions in the A-X Band of OH.
Schewe, H Christian; Zhang, Dongdong; Meijer, Gerard; Field, Robert W; Sartakov, Boris G; Groenenboom, Gerrit C; van der Avoird, Ad; Vanhaecke, Nicolas
2016-04-15
An experimental method is demonstrated that allows determination of the ratio between the electric (E1) and magnetic (M1) transition dipole moments in the A-X band of OH, including their relative sign. Although the transition strengths differ by more than 3 orders of magnitude, the measured M1-to-E1 ratio agrees with the ratio of the ab initio calculated values to within 3%. The relative sign is found to be negative, also in agreement with theory.
NASA Astrophysics Data System (ADS)
Tian, Wen-Yan; Kuang, Xiao-Yu; Li, Hui-Fang; Li, Yan-Fang; Ying-Li
2009-01-01
A theoretical method for studying the inter-relation between the local structure and EPR spectra is established by diagonalizing the complete energy matrices. For [M(H 2O) 6]XCl 6:Mn 2+ (M = Zn, Mg, Cd, Ca; X = Pt, Sn) systems, the calculated results demonstrate that the local structures around the octahedral Mn 2+ centers in the doped systems are very similar despite of the host crystals being different. Furthermore, it is shown that the EPR zero-field parameter D depends simultaneously on the local structure parameters R and θ while ( a - F) depends mainly on R, whether the doped systems are at liquid-nitrogen temperature or room temperature.
Nakamura, Nori; Hirai, Yuko; Kodama, Yoshiaki
2012-03-01
The electron paramagnetic resonance (EPR, or electron spin resonance) method was used to measure CO₂⁻· radicals recorded in tooth enamel by exposure to atomic-bomb gamma rays. The EPR-estimated doses (i.e. ⁶⁰Co gamma-ray equivalent dose) were generally in good correlation with cytogenetic data of the same survivors, whereas plots of EPR-estimated dose or cytogenetically estimated dose against DS02 doses turned out to scatter more widely. Because those survivors whose EPR doses were higher (or lower) than DS02 doses tended to show also higher (or lower) responses for cytogenetic responses, the apparent variation appears primarily due to problems in individual DS02 doses rather than the measurement errors associated with the EPR or cytogenetic technique. A part of the enamel samples were also used for evaluation of neutron doses by measuring ⁴¹Ca/⁴⁰Ca ratios using the accelerator mass spectrometry technique. The results for the measured ratios were on average ~85 % of the calculated ratios by DS02 (but within the 95 % confidence bounds of the simulated results), which lends support to DS02-derived neutron doses to the survivors.
Electron paramagnetic resonance in Cu-doped ZnO
NASA Astrophysics Data System (ADS)
Buchheit, R.; Acosta-Humánez, F.; Almanza, O.
2016-04-01
In this work, ZnO and Cu-doped ZnO nanoparticles (Zn1-xCuxO, x = 3%), with a calcination temperature of 500∘C were synthesized using the sol-gel method. The particles were analyzed using atomic absorption spectroscopy (AAS), X-ray diffraction (XRD) and electron paramagnetic resonance (EPR) at X-band, measurement in a temperature range from 90 K to room temperature. AAS confirmed a good correspondence between the experimental doping concentration and the theoretical value. XRD reveals the presence of ZnO phase in hexagonal wurtzite structure and a nanoparticle size for the samples synthesized. EPR spectroscopy shows the presence of point defects in both samples with g-values of g = 1.959 for shallow donors and g = 2.004 for ionized vacancies. It is important when these materials are required have been used as catalysts, as suggested that it is not necessary prepare them at higher temperature. A simulation of the Cu EPR signal using an anisotropic spin Hamiltonian was performed and showed good coincidence with the experimental spectra. It was shown that Cu2+ ions enter interstitial octahedral sites of orthorhombic symmetry in the wurtzite crystal structure. Temperature dependence of the EPR linewidth and signal intensity shows a paramagnetic behavior of the sample in the measurement range. A Néel temperature TN = 78 ± 19 K was determined.
NASA Astrophysics Data System (ADS)
D'Andrea, M.; Lotti, S.; Macculi, C.; Piro, L.; Argan, A.; Gatti, F.
2017-12-01
ATHENA is a large X-ray observatory, planned to be launched by ESA in 2028 towards an L2 orbit. One of the two instruments of the payload is the X-IFU: a cryogenic spectrometer based on a large array of TES microcalorimeters, able to perform integral field spectrography in the 0.2-12 keV band (2.5 eV FWHM at 6 keV). The X-IFU sensitivity is highly degraded by the particle background expected in the L2 orbit, which is induced by primary protons of both galactic and solar origin, and mostly by secondary electrons. To reduce the particle background level and enable the mission science goals, the instrument incorporates a Cryogenic AntiCoincidence detector (CryoAC). It is a 4 pixel TES based detector, placed < 1 mm below the main array. In this paper we report a scientific assessment of the CryoAC observational capabilities in the hard X-ray band (E > 10 keV). The aim of the study has been to understand if the present detector design can be improved in order to enlarge the X-IFU scientific capability on an energy band wider than the TES array. This is beyond the CryoAC baseline, being this instrument aimed to operate as anticoincidence particle detector and not conceived to perform X-ray observations.
THE VIEW FROM THE TRENCHES: PART 2–TECHNICAL CONSIDERATIONS FOR EPR SCREENING
Nicolalde, Roberto J.; Gougelet, Robert M.; Rea, Michael; Williams, Benjamin B.; Dong, Ruhong; Kmiec, Maciej M.; Lesniewski, Piotr N.; Swartz, Harold M.
2014-01-01
There is growing awareness of the need for methodologies that can be used retrospectively to provide the biodosimetry needed to carry out screening and triage immediately after an event in which large numbers of people have potentially received clinically significant doses of ionizing radiation. The general approach to developing such methodologies has been a technology centric one, often ignoring the system integrations considerations that are key to their effective use. In this study an integrative approach for the evaluation and development of a physical biodosimetry technology was applied based on in vivo electron paramagnetic resonance (EPR) dosimetry. The EPR measurements are based on physical changes in tissues whose magnitudes are not affected by the factors that can confound biologically-based assessments. In this study the use of a pilot simulation exercise to evaluate an experimental EPR system and gather stakeholders’ feedback early on in the development process is described. The exercise involved: ten non-irradiated participants, representatives from a local fire department; Department of Homeland Security certified exercise evaluators, EPR experts, physicians; and a human factors engineer. Stakeholders were in agreement that the EPR technology in its current state of development could be deployed for the screening of mass casualties. Furthermore, stakeholders’ recommendations will be prioritized and incorporated in future developments of the EPR technique. While the results of this exercise were aimed specifically at providing feedback for the development of EPR dosimetry for screening mass casualties, the methods and lessons learned are likely to be applicable to other biodosimetric methods. PMID:20065674
The localized effect of the Bi level on the valence band in the dilute bismuth GaBixAs1-x alloy
NASA Astrophysics Data System (ADS)
Zhao, Chuan-Zhen; Zhu, Min-Min; Wang, Jun; Wang, Sha-Sha; Lu, Ke-Qing
2018-05-01
The research on the temperature dependence of the band gap energy of the dilute bismuth GaBixAs1-x alloy has been done. It is found that its temperature insensitiveness is due to the enhanced localized character of the valence band state and the small decrease of the temperature coefficient for the conduction band minimum (CBM). The enhanced localized character of the valence band state is the main factor. In order to describe the localized effect of the Bi levels on the valence band, the localized energy is introduced into the Varshni's equation. It is found that the effect of the localized Bi level on the valence band becomes strong with increasing Bi content. In addition, it is found that the pressure dependence of the band gap energy of GaBixAs1-x does not seem to be influenced by the localized Bi levels. It is due to two factors. One is that the pressure dependence of the band gap energy is mainly determined by the D CBM of GaBixAs1-x. The D CBM of GaBixAs1-x is not influenced by the localized Bi levels. The other is that the small variation of the pressure coefficient for the D valence band maximum (VBM) state of GaBixAs1-x can be cancelled by the variation of the pressure coefficient for the D CBM state of GaBixAs1-x.
Breath air measurement using wide-band frequency tuning IR laser photo-acoustic spectroscopy
NASA Astrophysics Data System (ADS)
Kistenev, Yury V.; Borisov, Alexey V.; Kuzmin, Dmitry A.; Bulanova, Anna A.; Boyko, Andrey A.; Kostyukova, Nadezhda Y.; Karapuzikov, Alexey A.
2016-03-01
The results of measuring of biomarkers in breath air of patients with broncho-pulmonary diseases using wide-band frequency tuning IR laser photo-acoustic spectroscopy and the methods of data mining are presented. We will discuss experimental equipment and various methods of intellectual analysis of the experimental spectra in context of above task. The work was carried out with partial financial support of the FCPIR contract No 14.578.21.0082 (ID RFMEFI57814X0082).
NASA Astrophysics Data System (ADS)
Calmet, J. F.; Carlin, F.; Nguyen, T. M.; Bousquet, S.; Quinot, P.
2002-03-01
In this paper, correlations between the elongation at break and the oxidation of chlorosulfonated polyethylene and ethylene propylene rubber (EPR) polymers in instrumentation and control cables irradiated at different dose rates are brought to evidence. During irradiation, the following phenomena are observed: an increase of oxygen consumption, a degradation of the mechanical properties and a reduction of the oxidation induction time (OIT) measured for EPR. A correlation between the mechanical properties and the OIT of the EPR has only been established in the case of irradiation at low dose rate. This reveals a difference in the oxidative degradation process at low and high dose rates. This study shows the possibility to assess the ageing of electric cables installed inside nuclear power plants by OIT measurements.
A Ka-band (32 GHz) beacon link experiment (KABLE) with Mars Observer
NASA Technical Reports Server (NTRS)
Riley, A. L.; Hansen, D. M.; Mileant, A.; Hartop, R. W.
1987-01-01
A proposal for a Ka-Band (32 GHz) Link Experiment (KABLE) with the Mars Observer mission was submitted to NASA. The experiment will rely on the fourth harmonic of the spacecraft X-band transmitter to generate a 33.6 GHz signal. The experiment will rely also on the Deep Space Network (DSN) receiving station equipped to simultaneously receive X- and Ka-band signals. The experiment will accurately measure the spacecraft-to-Earth telecommunication link performance at Ka-band and X-band (8.4 GHz).
Hematite from Natural Iron Stones as Microwave Absorbing Material on X-Band Frequency Ranges
NASA Astrophysics Data System (ADS)
Zainuri, Mochamad
2017-05-01
This study has been investigated the effect of hematite as microwave absorbing materials (RAM) on X-Band frequency ranges. Hematite was succesfully processed by coprecipitation method and calcined at 500 °C for 5 hour. It was synthesized from natural iron stones from Tanah Laut, South Kalimantan, Indonesia. The products were characterized by X-ray diffraxtion (XRD), conductivity measurement, Vibrating Sample Magnetometer (VSM), and Vector Network Analyzer (VNA). The result was shown that hematite has conductivity value on (2.5-3).10-7 S/cm and be included as dielectric materials. The hysterisis curve was shown that hematite was a super paramagnetic materials. The product was mixed on paint with procentage 10% of total weight and coated on steel grade AH36 with spray methods. Then, the maximum of reflection loss on x - band’s frequency range (8,2-12,4) GHz was -7 dB on frequency of 10.5 GHz. It mean that almost 50% electromagnetic energy was absorbed by hematite.
NASA Astrophysics Data System (ADS)
Sahu, Indra D.; Hustedt, Eric J.; Ghimire, Harishchandra; Inbaraj, Johnson J.; McCarrick, Robert M.; Lorigan, Gary A.
2014-12-01
An EPR membrane alignment technique was applied to measure distance and relative orientations between two spin labels on a protein oriented along the surface of the membrane. Previously we demonstrated an EPR membrane alignment technique for measuring distances and relative orientations between two spin labels using a dual TOAC-labeled integral transmembrane peptide (M2δ segment of Acetylcholine receptor) as a test system. In this study we further utilized this technique and successfully measured the distance and relative orientations between two spin labels on a membrane peripheral peptide (antimicrobial peptide magainin-2). The TOAC-labeled magainin-2 peptides were mechanically aligned using DMPC lipids on a planar quartz support, and CW-EPR spectra were recorded at specific orientations. Global analysis in combination with rigorous spectral simulation was used to simultaneously analyze data from two different sample orientations for both single- and double-labeled peptides. We measured an internitroxide distance of 15.3 Å from a dual TOAC-labeled magainin-2 peptide at positions 8 and 14 that closely matches with the 13.3 Å distance obtained from a model of the labeled magainin peptide. In addition, the angles determining the relative orientations of the two nitroxides have been determined, and the results compare favorably with molecular modeling. This study demonstrates the utility of the technique for proteins oriented along the surface of the membrane in addition to the previous results for proteins situated within the membrane bilayer.
High-field EPR on membrane proteins - crossing the gap to NMR.
Möbius, Klaus; Lubitz, Wolfgang; Savitsky, Anton
2013-11-01
In this review on advanced EPR spectroscopy, which addresses both the EPR and NMR communities, considerable emphasis is put on delineating the complementarity of NMR and EPR concerning the measurement of molecular interactions in large biomolecules. From these interactions, detailed information can be revealed on structure and dynamics of macromolecules embedded in solution- or solid-state environments. New developments in pulsed microwave and sweepable cryomagnet technology as well as ultrafast electronics for signal data handling and processing have pushed to new horizons the limits of EPR spectroscopy and its multifrequency extensions concerning the sensitivity of detection, the selectivity with respect to interactions, and the resolution in frequency and time domains. One of the most important advances has been the extension of EPR to high magnetic fields and microwave frequencies, very much in analogy to what happens in NMR. This is exemplified by referring to ongoing efforts for signal enhancement in both NMR and EPR double-resonance techniques by exploiting dynamic nuclear or electron spin polarization via unpaired electron spins and their electron-nuclear or electron-electron interactions. Signal and resolution enhancements are particularly spectacular for double-resonance techniques such as ENDOR and PELDOR at high magnetic fields. They provide greatly improved orientational selection for disordered samples that approaches single-crystal resolution at canonical g-tensor orientations - even for molecules with small g-anisotropies. Exchange of experience between the EPR and NMR communities allows for handling polarization and resolution improvement strategies in an optimal manner. Consequently, a dramatic improvement of EPR detection sensitivity could be achieved, even for short-lived paramagnetic reaction intermediates. Unique structural and dynamic information is thus revealed that can hardly be obtained by any other analytical techniques. Micromolar
Yang, Lei; Fu, Qi; Wang, Wenhui; Huang, Jian; Huang, Jianliu; Zhang, Jingyu; Xiang, Bin
2015-06-21
"Band gap engineering" in two-dimensional (2D) materials plays an important role in tailoring their physical and chemical properties. The tuning of the band gap is typically achieved by controlling the composition of the semiconductor alloys. However, large-area preparation of 2D alloys remains a major challenge. Here, we report the large-area synthesis of high-quality monolayered MoS2(1-x)Se2x with a size coverage of hundreds of microns using a chemical vapor deposition method. The photoluminescence (PL) spectroscopy results confirm the tunable band gap in MoS2(1-x)Se2x, which is modulated by varying the Se content. Atomic-scale analysis was performed and the chemical composition was characterized using high-resolution scanning transmission electron microscopy and X-ray photoemission spectroscopy. With the introduction of Se into monolayered MoS2, it leads to enhanced catalytic activity in an electrochemical reaction for hydrogen generation, compared to monolayered MoS2 and MoSe2. It is promising as a potential alternative to expensive noble metals.
NASA Technical Reports Server (NTRS)
Mysoor, N. R.; Mueller, R. O.
1991-01-01
This article summarizes the design concepts, analyses, and development of an X-band (8145 MHz) transponder low-loss linear phase modulator for deep space spacecraft applications. A single-section breadboard circulator-coupled reflection phase modulator has been analyzed, fabricated, and evaluated. A linear phase deviation of 92 deg with a linearity tolerance of +/- 8 percent was measured for this modulator from 8257 MHz to 8634 MHz over the temperature range -20 to 75 C. The measured insertion loss and the static delay variation with temperature were 2 +/- 0.3 dB and 0.16 psec/ C, respectively. Based on this design, cascaded sections have been modeled, and simulations were performed to provide an X-band deep space transponder (DST) phase modulator with +/- 2.5 radians (+/- 143 deg) of peak phase deviation to accommodate downlink signal modulation with composite telemetry data and ranging, with a deviation linearity tolerance of +/- 8 percent and insertion loss of less than 10 +/- 0.5 dB. A two-section phase modulator using constant gamma hyperabrupt varactors and an efficient modulator driver circuit was breadboarded. The measured results satisfy the DST phase-modulator requirements and show excellent agreement with the predicted results.
Performance of a Wideband Cadmium Ferrite Microstrip Patch Antenna in the X-Band Region
NASA Astrophysics Data System (ADS)
Bhongale, S. R.; Ingavale, H. R.; Shinde, T. J.; Vasambekar, P. N.
2018-01-01
Magnesium-substituted cadmium ferrites with the chemical composition Mg x Cd1- x Fe2O4 ( x = 0, 0.4 and 0.8) were prepared by an oxalate co-precipitation method under microwave sintering technique. The structural properties of ferrites were studied by x-ray diffraction, Fourier transform infrared spectroscopy and field emission scanning electron microscope techniques. The scattering parameters such as reflection coefficient ( S 11) and transmission coefficient ( S 21) at microwave frequencies of palletized ferrites were measured by using a vector network analyzer. The software module 85071E followed by scattering parameters was used to determine the electromagnetic properties of the ferrites. The values determined for electromagnetic parameters such as the real part of permittivity ( ɛ'), permeability ( μ'), dielectric loss tangent (tan δ e) and magnetic loss tangent (tan δ m) of synthesized ferrites were used to design rectangular microstrip patch antennas. The performance of magnesium-substituted Cd ferrites as substrate for microstrip patch antennas was investigated. The antenna parameters such as return loss, bandwidth, voltage standing wave ratio, Smith chart and radiation pattern were studied. It is found that the Cd ferrite has applicability as a substrate for wideband antennas in the X-band region.
Seventy Years of the EPR Paradox
NASA Astrophysics Data System (ADS)
Kupczynski, Marian
2006-11-01
In spite of the fact that statistical predictions of quantum theory (QT) can only be tested if large amount of data is available a claim has been made that QT provides the most complete description of an individual physical system. Einstein's opposition to this claim and the paradox he presented in the article written together with Podolsky and Rosen in 1935 inspired generations of physicists in their quest for better understanding of QT. Seventy years after EPR article it is clear that without deep understanding of the character and limitations of QT one may not hope to find a meaningful unified theory of all physical interactions, manipulate qubits or construct a quantum computer.. In this paper we present shortly the EPR paper, the discussion, which followed it and Bell inequalities (BI). To avoid various paradoxes we advocate purely statistical contextual interpretation (PSC) of QT. According to PSC a state vector is not an attribute of a single electron, photon, trapped ion or quantum dot. A value of an observable assigned to a physical system has only a meaning in a context of a particular physical experiment PSC does not provide any mental space-time picture of sub phenomena. The EPR paradox is avoided because the reduction of the state vector in the measurement process is a passage from a description of the whole ensemble of the experimental results to a particular sub-ensemble of these results. We show that the violation of BI is neither a proof of the completeness of QT nor of its non-locality. Therefore we rephrase the EPR question and ask whether QT is "predictably "complete or in other words does it provide the complete description of experimental data. To test the "predictable completeness" it is not necessary to perform additional experiments it is sufficient to analyze more in detail the existing experimental data by using various non-parametric purity tests and other specific statistical tools invented to study the fine structure the time-series.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Dantas, Noelio Oliveira; Lima Fernandes, Guilherme de; Almeida Silva, Anielle Christine
2014-09-29
In this study, we synthesized Cd{sub 1−x}Mn{sub x}Te ultrasmall quantum dots (USQDs) in SiO{sub 2}-Na{sub 2}CO{sub 3}-Al{sub 2}O{sub 3}-B{sub 2}O{sub 3} glass system using the fusion method. Growth of these Cd{sub 1−x}Mn{sub x}Te USQDs was confirmed by optical absorption, atomic force microscopy (AFM), magnetic force microscopy (MFM), scanning transmission electron microscopy (TEM), and electron paramagnetic resonance (EPR) measurements. The blueshift of absorption transition with increasing manganese concentration gives evidence of incorporation of manganese ions (Mn{sup 2+}) in CdTe USQDs. AFM, TEM, and MFM confirmed, respectively, the formation of high quality Cd{sub 1−x}Mn{sub x}Te USQDs with uniformly distributed size and magneticmore » phases. Furthermore, EPR spectra showed six lines associated to the S = 5/2 spin half-filled d-state, characteristic of Mn{sup 2+}, and confirmed that Mn{sup 2+} are located in the sites core and surface of the CdTe USQD. Therefore, synthesis of high quality Cd{sub 1−x}Mn{sub x}Te USQDs may allow the control of optical and magnetic properties.« less
Fu, Qi; Yang, Lei; Wang, Wenhui; Han, Ali; Huang, Jian; Du, Pingwu; Fan, Zhiyong; Zhang, Jingyu; Xiang, Bin
2015-08-26
The first realization of a tunable band-gap in monolayer WS2(1-x) Se2x is demonstrated. The tuning of the bandgap exhibits a strong dependence of S and Se content, as proven by PL spectroscopy. Because of its remarkable electronic structure, monolayer WS2(1-x) Se2x exhibits novel electrochemical catalytic activity and offers long-term electrocatalytic stability for the hydrogen evolution reaction. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
EPR detection of foods preserved with ionizing radiation
NASA Astrophysics Data System (ADS)
Stachowicz, W.; Burlinska, G.; Michalik, J.
1998-06-01
The applicability of the epr technique for the detection of dried vegetables, mushrooms, some spices, flavour additives and some condiments preserved with ionizing radiation is discussed. The epr signals recorded after exposure to gamma rays and to beams of 10 MeV electrons from linac are stable, intense and specific enough as compared with those observed with nonirradiated samples and could be used for the detection of irradiation. However, stability of radiation induced epr signals produced in these foods depends on storage condition. No differences in shapes (spectral parameters) and intensities of the epr spectra recorded with samples exposed to the same doses of gamma rays ( 60Co) and 10 MeV electrons were observed
Khan, Nadeem; Mupparaju, Sriram; Hou, Huagang; Williams, Benjamin B; Swartz, Harold
2012-02-15
Tumor hypoxia plays a vital role in therapeutic resistance. Consequently, measurements of tumor pO(2) could be used to optimize the outcome of oxygen-dependent therapies, such as, chemoradiation. However, the potential optimizations are restricted by the lack of methods to repeatedly and quantitatively assess tumor pO(2) during therapies, particularly in gliomas. We describe the procedures for repeated measurements of orthotopic glioma pO(2) by multi-site electron paramagnetic resonance (EPR) oximetry. This oximetry approach provides simultaneous measurements of pO(2) at more than one site in the glioma and contralateral cerebral tissue. The pO(2) of intracerebral 9L, C6, F98 and U251 tumors, as well as contralateral brain, were measured repeatedly for five consecutive days. The 9L glioma was well oxygenated with pO(2) of 27-36 mm Hg, while C6, F98 and U251 glioma were hypoxic with pO(2) of 7-12mm Hg. The potential of multi-site EPR oximetry to assess temporal changes in tissue pO(2) was investigated in rats breathing 100% O(2). A significant increase in F98 tumor and contralateral brain pO(2) was observed on day 1 and day 2, however, glioma oxygenation declined on subsequent days. In conclusion, EPR oximetry provides the capability to repeatedly assess temporal changes in orthotopic glioma pO(2). This information could be used to test and optimize the methods being developed to modulate tumor hypoxia. Furthermore, EPR oximetry could be potentially used to enhance the outcome of chemoradiation by scheduling treatments at times of increase in glioma pO(2). Copyright © 2011 Elsevier B.V. All rights reserved.
The Mars Global Surveyor Ka-Band Link Experiment (MGS/KaBLE-II)
NASA Astrophysics Data System (ADS)
Morabito, D.; Butman, S.; Shambayati, S.
1999-01-01
The Mars Global Surveyor (MGS) spacecraft, launched on November 7, 1996, carries an experimental space-to-ground telecommunications link at Ka-band (32 GHz) along with the primary X-band (8.4-GHz) downlink. The signals are simultaneously transmitted from a 1.5-m-diameter parabolic antenna on MGS and received by a beam-waveguide (BWG) research and development (R&D) 34-meter a ntenna located in NASA's Goldstone Deep Space Network (DSN) complex near Barstow, California. This Ka-band link experiment (KaBLE-II) allows the performances of the Ka-band and X-band signals to be compared under nearly identical conditions. The two signals have been regularly tracked during the past 2 years. This article presents carrier-signal-level data (P_c/N_o) for both X-band and Ka-band acquired over a wide range of station elevation angles, weather conditions, and solar elongation angles. The cruise phase of the mission covered the period from launch (November 7, 1996) to Mars orbit capture (September 12, 1997). Since September 12, 1997, MGS has been in orbit around Mars. The measurements confirm that Ka-band could increase data capacity by at least a factor of three (5 dB) as compared with X-band. During May 1998, the solar corona experiment, in which the effects of solar plasma on the X-band and Ka-band links were studied, was conducted. In addition, frequency and difference frequency (f_x - f_(Ka)/3.8), ranging, and telemetry data results are presented. MGS/KaBLE-II measured signal strengths (for 54 percent of the experiments conducted) that were in reasonable agreement with predicted values based on preflight knowledge, and frequency residuals that agreed between bands and whose statistics were consistent with expected noise sources. For passes in which measured signal strengths disagreed with predicted values, the problems were traced to known deficiencies, for example, equipment operating under certain conditions, such as a cold Ka-band solid-state power amplifier (SSPA
Analyzing shear band formation with high resolution X-ray diffraction
DOE Office of Scientific and Technical Information (OSTI.GOV)
Pagan, Darren C.; Obstalecki, Mark; Park, Jun-Sang
Localization of crystallographic slip into shear bands during uniaxial compression of a copper single crystal is studied using very far-field high-energy diffraction microscopy (vff-HEDM). Diffracted intensity was collected in-situ as the crystal deformed using a unique mobile detector stage that provided access to multiple diffraction peaks with high-angular resolution. From the diffraction data, single crystal orientation pole figures (SCPFs) were generated and are used to track the evolution of the distribution of lattice orientation that develops as slip localizes. To aid the identification of 'signatures' of shear band formation and analyze the SCPF data, a model of slip-driven lattice reorientationmore » within shear bands is introduced. Confidence is built in conclusions drawn from the SCPF data about the character of internal slip localization through comparisons with strain fields on the sample surface measured simultaneously using digital image correlation. From the diffraction data, we find that the active slip direction and slip plane are not directly aligned with the orientation of the shear bands that formed. In fact, by extracting the underlying slip system activity from the SCPF data, we show that intersecting shear bands measured on the surface of the sample arise from slip primarily on the same underlying single slip system. These new vff-HEDM results raise significant questions on the use of surface measurements for slip system activity estimation. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.« less
Analyzing shear band formation with high resolution X-ray diffraction
Pagan, Darren C.; Obstalecki, Mark; Park, Jun-Sang; ...
2018-01-10
Localization of crystallographic slip into shear bands during uniaxial compression of a copper single crystal is studied using very far-field high-energy diffraction microscopy (vff-HEDM). Diffracted intensity was collected in-situ as the crystal deformed using a unique mobile detector stage that provided access to multiple diffraction peaks with high-angular resolution. From the diffraction data, single crystal orientation pole figures (SCPFs) were generated and are used to track the evolution of the distribution of lattice orientation that develops as slip localizes. To aid the identification of ‘signatures’ of shear band formation and analyze the SCPF data, a model of slip-driven lattice reorientationmore » within shear bands is introduced. Confidence is built in conclusions drawn from the SCPF data about the character of internal slip localization through comparisons with strain fields on the sample surface measured simultaneously using digital image correlation. From the diffraction data, we find that the active slip direction and slip plane are not directly aligned with the orientation of the shear bands that formed. In fact, by extracting the underlying slip system activity from the SCPF data, we show that intersecting shear bands measured on the surface of the sample arise from slip primarily on the same underlying single slip system. These new vff-HEDM results raise significant questions on the use of surface measurements for slip system activity estimation.« less
NASA Astrophysics Data System (ADS)
Breeson, Andrew C.; Sankar, Gopinathan; Goh, Gregory K. L.; Palgrave, Robert G.
2017-11-01
A method of quantitative phase analysis using valence band X-ray photoelectron spectra is presented and applied to the analysis of TiO2 anatase-rutile mixtures. The valence band spectra of pure TiO2 polymorphs were measured, and these spectral shapes used to fit valence band spectra from mixed phase samples. Given the surface sensitive nature of the technique, this yields a surface phase fraction. Mixed phase samples were prepared from high and low surface area anatase and rutile powders. In the samples studied here, the surface phase fraction of anatase was found to be linearly correlated with photocatalytic activity of the mixed phase samples, even for samples with very different anatase and rutile surface areas. We apply this method to determine the surface phase fraction of P25 powder. This method may be applied to other systems where a surface phase fraction is an important characteristic.
Effects of microstructure banding on hydrogen assisted fatigue crack growth in X65 pipeline steels
DOE Office of Scientific and Technical Information (OSTI.GOV)
Ronevich, Joseph A.; Somerday, Brian P.; San Marchi, Chris W.
Banded ferrite-pearlite X65 pipeline steel was tested in high pressure hydrogen gas to evaluate the effects of oriented pearlite on hydrogen assisted fatigue crack growth. Test specimens were oriented in the steel pipe such that cracks propagated either parallel or perpendicular to the banded pearlite. The ferrite-pearlite microstructure exhibited orientation dependent behavior in which fatigue crack growth rates were significantly lower for cracks oriented perpendicular to the banded pearlite compared to cracks oriented parallel to the bands. Thus the reduction of hydrogen assisted fatigue crack growth across the banded pearlite is attributed to a combination of crack-tip branching and impededmore » hydrogen diffusion across the banded pearlite.« less
Effects of microstructure banding on hydrogen assisted fatigue crack growth in X65 pipeline steels
Ronevich, Joseph A.; Somerday, Brian P.; San Marchi, Chris W.
2015-09-10
Banded ferrite-pearlite X65 pipeline steel was tested in high pressure hydrogen gas to evaluate the effects of oriented pearlite on hydrogen assisted fatigue crack growth. Test specimens were oriented in the steel pipe such that cracks propagated either parallel or perpendicular to the banded pearlite. The ferrite-pearlite microstructure exhibited orientation dependent behavior in which fatigue crack growth rates were significantly lower for cracks oriented perpendicular to the banded pearlite compared to cracks oriented parallel to the bands. Thus the reduction of hydrogen assisted fatigue crack growth across the banded pearlite is attributed to a combination of crack-tip branching and impededmore » hydrogen diffusion across the banded pearlite.« less
Mini-RF S- and X-Band Bistatic Radar Observations of the Moon
NASA Astrophysics Data System (ADS)
Patterson, G. W.; Carter, L. M.; Stickle, A. M.; Cahill, J. T. S.; Nolan, M. C.; Morgan, G. A.; Schroeder, D. M.; Mini-RF Team
2018-04-01
The Mini-RF instrument onboard the NASA LRO mission is collecting S- and X-band bistatic radar data to provide new insights regarding regolith development on the Moon, the diversity of lunar volcanism, and the current inventory of polar ice.
Low-loss negative index metamaterials for X, Ku, and K microwave bands
DOE Office of Scientific and Technical Information (OSTI.GOV)
Lee, David A.; Vedral, L. James; Smith, David A.
2015-04-15
Low-loss, negative-index of refraction metamaterials were designed and tested for X, Ku, and K microwave frequency bands. An S-shaped, split-ring resonator was used as a unit cell to design homogeneous slabs of negative-index metamaterials. Then, the slabs of metamaterials were cut unto prisms to measure experimentally the negative index of refraction of a plane electromagnetic wave. Theoretical simulations using High-Frequency Structural Simulator, a finite element equation solver, were in good agreement with experimental measurements. The negative index of refraction was retrieved from the angle- and frequency-dependence of the transmitted intensity of the microwave beam through the metamaterial prism and comparedmore » well to simulations; in addition, near-field electromagnetic intensity mapping was conducted with an infrared camera, and there was also a good match with the simulations for expected frequency ranges for the negative index of refraction.« less
Nakagawa, Kouichi; Hara, Hideyuki
2016-01-01
We investigated the antioxidant activities and locations of stable paramagnetic species in dry (or drying) shiitake mushroom (Lentinus edodes) using continuous wave (CW) electron paramagnetic resonance (EPR) and 9 GHz EPR imaging. CW 9 GHz EPR detected paramagnetic species (peak-to-peak linewidth (ΔHpp) = 0.57 mT) in the mushroom. Two-dimensional imaging of the sharp line using a 9 GHz EPR imager showed that the species were located in the cap and shortened stem portions of the mushroom. No other location of the species was found in the mushroom. However, radical locations and concentrations varied along the cap of the mushroom. The 9 GHz EPR imaging determined the exact location of stable paramagnetic species in the shiitake mushroom. Distilled water extracts of the pigmented cap surface and the inner cap of the mushroom showed similar antioxidant activities that reduced an aqueous solution of 0.1 mM 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl. The present results suggest that the antioxidant activities of the edible mushroom extracts are much weaker than those of ascorbic acid. Thus, CW EPR and EPR imaging revealed the location and distribution of stable paramagnetic species and the antioxidant activities in the shiitake mushroom for the first time.
EPR study on non- and gamma-irradiated herbal pills
NASA Astrophysics Data System (ADS)
Aleksieva, K.; Lagunov, O.; Dimov, K.; Yordanov, N. D.
2011-06-01
The results of EPR studies on herbal pills of marigold, hawthorn, yarrow, common balm, tutsan, nettle and thyme before and after gamma-irradiation are reported. Before irradiation all samples exhibit one weak singlet EPR line with a g-factor of 2.0048±0.0005. After irradiation herbal pills could be separated in two groups according to their EPR spectra. Radiation-induced free radicals in pills of marigold, yarrow, nettle, tutsan and thyme could be attributed mainly to saccharide excipients. Tablets of hawthorn and common balm show "cellulose-like" EPR spectrum, superimposed on partly resolved carbohydrate spectrum, due to the active part (herb) and inulin, which is present in the pills as an excipient. Fading study of the radiation-induced EPR signals confirms that sugar radicals are more stable than cellulose species. The reported results show that the presence of characteristic EPR spectra of herbal pills due to excipients or active part can be used as unambiguous proof of radiation processing within 35 or more days after irradiation.
An X-band phase-locked relativistic backward wave oscillator
DOE Office of Scientific and Technical Information (OSTI.GOV)
Wu, Y.; Science and Technology on High Power Microwave Laboratory, Mianyang 621900; Li, Z. H.
2015-08-15
For the purpose of coherent high power microwave combining at high frequency band, an X-band phase-locked relativistic backward wave oscillator is presented and investigated. The phase-locking of the oscillator is accomplished by modulation of the electron beam before it reaches the oscillator. To produce a bunched beam with an acceptable injected RF power requirement, an overmoded input cavity is employed to provide initial density modulation. And a buncher cavity is introduced to further increase the modulation depth. When the beam enters the oscillator, the modulation depth is enough to lock the frequency and phase of the output microwave generated bymore » the oscillator. Particle-in-cell simulation shows that an input power of 90 kW is sufficient to lock the frequency and phase of 1.5 GW output microwave with locking bandwidth of 60 MHz.« less
Monoanionic molybdenum and tungsten tris(dithiolene) complexes: a multifrequency EPR study.
Sproules, Stephen; Banerjee, Priyabrata; Weyhermüller, Thomas; Yan, Yong; Donahue, James P; Wieghardt, Karl
2011-08-01
Numerous Mo and W tris(dithiolene) complexes in varying redox states have been prepared and representative examples characterized crystallographically: [M(S(2)C(2)R(2))(3)](z) [M = Mo, R = Ph, z = 0 (1) or 1- (2); M = W, R = Ph, z = 0 (4) or 1- (5); R = CN, z = 2-, M = Mo (3) or W (6)]. Changes in dithiolene C-S and C-C bond lengths for 1 versus 2 and 4 versus 5 are indicative of ligand reduction. Trigonal twist angles (Θ) and dithiolene fold angles (α) increase and decrease, respectively, for 2 versus 1, 5 versus 4. Cyclic voltammetry reveals generally two reversible couples corresponding to 0/1- and 1-/2- reductions. The electronic structures of monoanionic molybdenum tris(dithiolene) complexes have been analyzed by multifrequency (S-, X-, Q-band) EPR spectroscopy. Spin-Hamiltonian parameters afforded by spectral simulation for each complex demonstrate the existence of two distinctive electronic structure types. The first is [Mo(IV)((A)L(3)(5-•))](1-) ((A)L = olefinic dithiolene, type A), which has the unpaired electron restricted to the tris(dithiolene) unit and is characterized by isotropic g-values and small molybdenum superhyperfine coupling. The second is formulated as [Mo(V)((B)L(3)(6-))](1-) ((B)L = aromatic dithiolene, type B) with spectra distinguished by a prominent g-anisotropy and hyperfine coupling consistent with the (d(z(2)))(1) paramagnet. The electronic structure disparity is also manifested in their electronic absorption spectra. The compound [W(bdt)(3)](1-) exhibits spin-Hamiltonian parameters similar to those of [Mo(bdt)(3)](1-) and thus is formulated as [W(V)((B)L(3)(6-))](1-). The EPR spectra of [W((A)L(3))](1-) display spin-Hamiltonian parameters that suggest their electronic structure is best represented by two resonance forms {[W(IV)((A)L(3)(5-•))](1-) ↔ [W(V)((A)L(3)(6-))](1-)}. The contrast with the corresponding [Mo(IV)((A)L(3)(5-•))](1-) complexes highlights tungsten's preference for higher oxidation states. © 2011 American
EPR: Some History and Clarification
NASA Astrophysics Data System (ADS)
Fine, Arthur
2002-04-01
Locality, separation and entanglement 1930s style. We’ll explore the background to the 1935 paper by Einstein, Podolsky and Rosen, how it was composed, the actual argument of the paper, the principles used, and how the paper was received by Schroedinger, and others.We’ll also look at Bohr’s response: the extent to which Bohr connects with what Einstein was after in EPR and the extent to EPR marks a shift in Bohr’s thinking about the quantum theory.
NASA Astrophysics Data System (ADS)
Zerentürk, A.; Açıkgöz, M.; Kazan, S.; Yıldız, F.; Aktaş, B.
2017-02-01
In this paper, we present the results of X-band EPR spectra of Co2+ ion doped rutile (TiO2) which is one of the most promising memristor material. We obtained the angular variation of spectra in three mutually perpendicular planes at liquid helium (7-13 K) temperatures. Since the impurity ions have ½ effective spin and 7/2 nuclear spin, a relatively simple spin Hamiltonian containing only electronic Zeeman and hyperfine terms was utilized. Two different methods were used in theoretical analysis. Firstly, a linear regression analysis of spectra based on perturbation theory was studied. However, this approach is not sufficient for analyzing Co+2 spectra and leads to complex eigenvectors for G and A tensors due to large anisotropy of eigenvalues. Therefore, all spectra were analyzed again with exact diagonalization of spin Hamiltonian and the high accuracy eigenvalues and eigenvectors of G and A tensors were obtained by taking into account the effect of small sample misalignment from the exact crystallographic planes due to experimental conditions. Our results show that eigen-axes of g and A tensors are parallel to crystallographic directions. Hence, our EPR experiments proves that Co2+ ions substitute for Ti4+ ions in lattice. The obtained principal values of g tensor are gx=2.110(6), gy=5.890(2), gz=3.725(7) and principal values of hyperfine tensor are Ax=42.4, Ay=152.7, Az=26 (in 10-4/cm).
Signature of Arctic first-year ice melt pond fraction in X-band SAR imagery
NASA Astrophysics Data System (ADS)
Fors, Ane S.; Divine, Dmitry V.; Doulgeris, Anthony P.; Renner, Angelika H. H.; Gerland, Sebastian
2017-03-01
In this paper we investigate the potential of melt pond fraction retrieval from X-band polarimetric synthetic aperture radar (SAR) on drifting first-year sea ice. Melt pond fractions retrieved from a helicopter-borne camera system were compared to polarimetric features extracted from four dual-polarimetric X-band SAR scenes, revealing significant relationships. The correlations were strongly dependent on wind speed and SAR incidence angle. Co-polarisation ratio was found to be the most promising SAR feature for melt pond fraction estimation at intermediate wind speeds (6. 2 m s-1), with a Spearman's correlation coefficient of 0. 46. At low wind speeds (0. 6 m s-1), this relation disappeared due to low backscatter from the melt ponds, and backscatter VV-polarisation intensity had the strongest relationship to melt pond fraction with a correlation coefficient of -0. 53. To further investigate these relations, regression fits were made both for the intermediate (R2fit = 0. 21) and low (R2fit = 0. 26) wind case, and the fits were tested on the satellite scenes in the study. The regression fits gave good estimates of mean melt pond fraction for the full satellite scenes, with less than 4 % from a similar statistics derived from analysis of low-altitude imagery captured during helicopter ice-survey flights in the study area. A smoothing window of 51 × 51 pixels gave the best reproduction of the width of the melt pond fraction distribution. A considerable part of the backscatter signal was below the noise floor at SAR incidence angles above ˜ 40°, restricting the information gain from polarimetric features above this threshold. Compared to previous studies in C-band, limitations concerning wind speed and noise floor set stricter constraints on melt pond fraction retrieval in X-band. Despite this, our findings suggest new possibilities in melt pond fraction estimation from X-band SAR, opening for expanded monitoring of melt ponds during melt season in the future.
[EPR study of iron status in human body during intensive physical activity].
Ibragimova, M I; Chushnikov, A I; Cherepnev, G V; Petukhov, V Iu; Zheglov, E P
2014-01-01
The iron metabolism was studied in serum blood samples collected from 26 professional sportsmen undergoing intensive physical exercises using EPR combined with haematological and biochemical laboratory tests. Only 23% of EPR spectra (n = 6) were practically normal while in the rest spectra additional abnormal absorption lines were detected. Presumably, the significant portion of new signals may be caused by different cytochromes. Moreover, the anisotropic signals with g1 approximately equal to 2.02; g2 approximately equal to 1.94 and g3 approximately equal to 1.86 registered in some spectra pointed to the sulfur-iron centers. There was nearly linear correlation between the concentration of Fe3+ in transfferin (Fe(3+)-Tf) obtained from the EPR spectra and the serum iron concentration measured by absorption photometry both for sportsmen and controls (healthy individuals and patients with different diseases). At equal serum iron concentrations the Fe(3+)-Tf level was higher in sportsmen than that in controls. The Pearson correlation coefficient (r) for Fe(3+)-Tf and serum iron values was equal to 0.89 in sportsmen versus r = 0.97 in controls. Additional new lines in serum EPR spectra of professional sportsmen prove the suitability of EPR assay for scheduled medical exams since routinebiochemical and haematological tests are insufficient to discover all abnormalities in iron metabolism under intensive physical exercises.
Photodissociation of PbI2 in the ultraviolet: analysis of the A rightarrow X band of PbI
NASA Astrophysics Data System (ADS)
Rodriguez, G.; Herring, C. M.; Fraser, R. D.; Eden, J. G.
1996-07-01
Emission and absorption studies of lead moniodide (PbI) have been carried out by photodissociation of PbI2 vapor at one of several wavelengths (193, 248, 266, 308, and 351 nm) in the ultraviolet. Strong emission on the A \\rightarrow X2 Pi 1/2 band (14400-22800 cm -1 ; 440 \\similar-or-less lambda \\similar-or-less 695 nm) occurs when PbI2 is photodissociated at 248 or 266 nm. Also, absorption bands attributed to the B \\leftarrow X2 Pi 1/2,3/2 , D \\leftarrow X2 Pi 1/2,3/2 , and E \\leftarrow X2 Pi 1/2,3/2 transitions of the diatomic molecule have been observed at 290 and 380, 225 and 265, and 203 and 240 nm, respectively, as have emission bands peaking at 397.6, 531.6, 582.0, 595.1, 639.7, 685.9, and 707.9 nm that appear to arise from PbI2 itself. Analysis and computer simulations of the A \\rightarrow X2 Pi 1/2 emission spectra have resulted in identifications for virtually all (>120) of the observed vibrational bandheads. Several spectroscopic constants for the A and the X2 Pi 1/2 states of PbI have been determined to be Te(A)=20659+/-130 cm-1 , omega e\\prime =132.2+/-1.0cm -1 , omega e\\prime xe\\prime =1.91+/-0.06cm -1 , omega e\\prime \\prime=160.3+/-0.6cm-1 , and omega e\\prime \\primexe \\prime\\prime=0.24+/-0.03cm -1 . Also, the difference between the equilibrium internuclear separations for the X2 Pi 1/2 and the A states has been determined to be Delta Re=0.45+/-0.05 . The spontaneous-emission lifetime for the PbI(A) state and the rate constant for quenching of this state by PbI2 (in two-body collisions) have been measured to be (94.3+/-8.8) ns and (4.3+/-0.4) \\times 10-10 cm3s -1 , respectively.
Cr3+-Doped Yb3Ga5O12 Nanophosphor: Synthesis, Optical, EPR, Studies
NASA Astrophysics Data System (ADS)
Singh, Vijay; Sivaramaiah, G.; Rao, J. L.; Singh, N.; Pathak, M. S.; Jirimali, H. D.; Singh, Pramod K.; Srivastava, Anoop K.; Dhoble, S. J.; Mohapatra, M.
2016-08-01
Gallium garnets of lanthanides are multifunctional materials especially known for their complicated structure and magnetic properties. In addition, with a suitable transition metal dopant ion, these matrices have been proved to be excellent materials for lasers. In particular, gallium garnet of ytterbium (Yb3Ga5O12) is known to possess excellent properties with regards to these applications. In this connection, Yb3Ga5O12 doped with Cr3+ nanophosphors were synthesized by a solution combustion route. The synthesized material was characterized by powder x-ray diffraction and scanning electron microscopy for phase purity and homogenous morphology. In order to ascertain the oxidation state of the doped ion, diffuse reflectance (DRF), photoluminescence (PL) and electron paramagnetic resonance (EPR) experiments were performed on the sample. The DRF and PL data suggested the stabilisation of the trivalent Cr ion in the matrix. The EPR spectra exhibited two resonance signals with effective g values at g ≈ 7.6 and 4. The EPR data corroborated the DRF and PL results, suggesting the stabilisation of Cr3+ in the matrix at octahedral-type geometries.
NASA Technical Reports Server (NTRS)
Slobin, S. D.
1987-01-01
The Deep Space Network (DSN) 64-meter antenna in Spain (DSN 63) has been calibrated prior to its upgrading to a 70-meter high efficiency configuration in preparation for the Voyager Neptune encounter in August 1989. The S-band (2285 MHz) and X-band (8420 MHz) effective area efficiency and system noise temperature calibrations were carried out during July 1986 to establish a baseline system performance for this station. It is expected that the 70-meter will result in at least a 1.9 dB G/T improvement at X-band relative to the 64-meter baseline reference.
EPR study on gamma-irradiated fruits dehydrated via osmosis
NASA Astrophysics Data System (ADS)
Yordanov, N. D.; Aleksieva, K.
2007-06-01
The shape and time stability of the electron paramagnetic resonance (EPR) spectra of non- and γ-irradiated papaya, melon, cherry and fig samples dehydrated via osmosis are reported. It is shown that non-irradiated samples are generally EPR silent whereas γ-irradiated exhibit "sugar-like" EPR spectra. The recorded EPR spectra are monitored for a period of 7 months after irradiation (stored at low humidity and in the dark). The results suggest longer period of unambiguous identification of the radiation processing of osmose dehydrated fruits. Therefore, the Protocol EN 13708,2001 issued by CEN is fully applicable for the studied fruit samples.
NASA Astrophysics Data System (ADS)
Yuan, Lei; Zhang, Hongpeng; Jia, Renxu; Guo, Lixin; Zhang, Yimen; Zhang, Yuming
2018-03-01
Energy band alignments between series band of Al-rich high-k materials (HfO2)x(Al2O3)1-x and β-Ga2O3 are investigated using X-Ray Photoelectron Spectroscopy (XPS). The results exhibit sufficient conduction band offsets (1.42-1.53 eV) in (HfO2)x(Al2O3)1-x/β-Ga2O3. In addition, it is also obtained that the value of Eg, △Ec, and △Ev for (HfO2)x(Al2O3)1-x/β-Ga2O3 change linearly with x, which can be expressed by 6.98-1.27x, 1.65-0.56x, and 0.48-0.70x, respectively. The higher dielectric constant and higher effective breakdown electric field of (HfO2)x(Al2O3)1-x compared with Al2O3, coupled with sufficient barrier height and lower gate leakage makes it a potential dielectric for high voltage β-Ga2O3 power MOSFET, and also provokes interest in further investigation of HfAlO/β-Ga2O3 interface properties.
Novel ZrO2 based ceramics stabilized by Fe2O3, SiO2 and Y2O3
NASA Astrophysics Data System (ADS)
Rada, S.; Culea, E.; Rada, M.
2018-03-01
Samples in the 5Fe2O3·10SiO2·xY2O3·(85-x)ZrO2 composition where x = 5, 10 and 15 mol% Y2O3 were synthesized and investigated by XRD, SEM, density measurements, FTIR, UV-Vis, EPR and PL spectroscopies. X-ray diffraction patterns confirm the presence of the tetragonal and cubic ZrO2 crystalline phases in all samples. The IR data show the overlaps of absorption bands assigned to Zrsbnd Osbnd Zr and Sisbnd Osbnd linkages in samples. UV-Vis and PL data indicate higher concentrations of intrinsic defects by doping with Y2O3 concentrations. The EPR spectra are characterized by two resonance lines situated at about g ∼ 4.3 and g ∼ 2 for lower Y2O3 contents.
Spin splitting in band structures of BiTeX (X=Cl, Br, I) monolayers
NASA Astrophysics Data System (ADS)
Hvazdouski, D. C.; Baranava, M. S.; Stempitsky, V. R.
2018-04-01
In systems with breaking of inversion symmetry a perpendicular electric field arises that interacts with the conduction electrons. It may give rise to electron state splitting even without influence of external magnetic field due to the spin-orbital interaction (SOI). Such a removal of the spin degeneracy is called the Rashba effect. Nanostructure with the Rashba effect can be part of a spin transistor. Spin degeneracy can be realized in a channel from a material of this type without additive of magnetic ions. Lack of additive increases the charge carrier mobility and reliability of the device. Ab initio simulations of BiTeX (X=Cl, Br, I) monolayers have been carried out using VASP wherein implemented DFT method. The study of this structures is of interest because such sort of structures can be used their as spin-orbitronics materials. The crystal parameters of BiTeCl, BiTeBr, BiTeI have been determined by the ionic relaxation and static calculations. It is necessary to note that splitting of energy bands occurs in case of SOI included. The values of the Rashba coefficient aR (in the range from 6.25 to 10.00 eV·Å) have high magnitudes for spintronics materials. Band structure of monolayers structures have ideal Rashba electron gas, i.e. there no other energy states near to Fermi level except Rashba states.
Mars Global Surveyor Ka-Band Frequency Data Analysis
NASA Astrophysics Data System (ADS)
Morabito, D.; Butman, S.; Shambayati, S.
2000-01-01
The Mars Global Surveyor (MGS) spacecraft, launched on November 7, 1996, carries an experimental space-to-ground telecommunications link at Ka-band (32 GHz) along with the primary X-band (8.4 GHz) downlink. The signals are simultaneously transmitted from a 1.5-in diameter parabolic high gain antenna (HGA) on MGS and received by a beam-waveguide (BWG) R&D 34-meter antenna located in NASA's Goldstone Deep Space Network (DSN) complex near Barstow, California. The projected 5-dB link advantage of Ka-band relative to X-band was confirmed in previous reports using measurements of MGS signal strength data acquired during the first two years of the link experiment from December 1996 to December 1998. Analysis of X-band and Ka-band frequency data and difference frequency (fx-fka)/3.8 data will be presented here. On board the spacecraft, a low-power sample of the X-band downlink from the transponder is upconverted to 32 GHz, the Ka-band frequency, amplified to I-W using a Solid State Power Amplifier, and radiated from the dual X/Ka HGA. The X-band signal is amplified by one of two 25 W TWTAs. An upconverter first downconverts the 8.42 GHz X-band signal to 8 GHz and then multiplies using a X4 multiplier producing the 32 GHz Ka-band frequency. The frequency source selection is performed by an RF switch which can be commanded to select a VCO (Voltage Controlled Oscillator) or USO (Ultra-Stable Oscillator) reference. The Ka-band frequency can be either coherent with the X-band downlink reference or a hybrid combination of the USO and VCO derived frequencies. The data in this study were chosen such that the Ka-band signal is purely coherent with the X-band signal, that is the downconverter is driven by the same frequency source as the X-band downlink). The ground station used to acquire the data is DSS-13, a 34-meter BWG antenna which incorporates a series of mirrors inside beam waveguide tubes which guide the energy to a subterranean pedestal room, providing a stable environment
Nature of the abnormal band gap narrowing in highly crystalline Zn1-xCoxO nanorods
NASA Astrophysics Data System (ADS)
Qiu, Xiaoqing; Li, Liping; Li, Guangshe
2006-03-01
Highly crystalline Zn1-xCoxO nanorods were prepared using a hydrothermal method. With increasing Co2+ dopant concentration, the lattice volume enlarged considerably, which is associated with the enhanced repulsive interactions of defect dipole moments on the wall surfaces. This lattice modification produced a significant decrease in band gap energies with its magnitude that followed the relationship, ΔEg=ΔE0•(e-x/B-1), where x and B are Co2+ dopant concentration and a constant, respectively. The abnormal band gap energies were indicated to originate from the sp-d exchange interactions that are proportional to the square of lattice volume.
Transient radical pairs studied by time-resolved EPR.
Bittl, Robert; Weber, Stefan
2005-02-25
Photogenerated short-lived radical pairs (RP) are common in biological photoprocesses such as photosynthesis and enzymatic DNA repair. They can be favorably probed by time-resolved electron paramagnetic resonance (EPR) methods with adequate time resolution. Two EPR techniques have proven to be particularly useful to extract information on the working states of photoinduced biological processes that is only difficult or sometimes even impossible to obtain by other types of spectroscopy. Firstly, transient EPR yields crucial information on the chemical nature and the geometry of the individual RP halves in a doublet-spin pair generated by a short laser pulse. This time-resolved method is applicable in all magnetic field/microwave frequency regimes that are used for continuous-wave EPR, and is nowadays routinely utilized with a time resolution reaching about 10 ns. Secondly, a pulsed EPR method named out-of-phase electron spin echo envelope modulation (OOP-ESEEM) is increasingly becoming popular. By this pulsed technique, the mutual spin-spin interaction between the RP halves in a doublet-spin pair manifests itself as an echo modulation detected as a function of the microwave-pulse spacing of a two-pulse echo sequence subsequent to a laser pulse. From the dipolar coupling, the distance between the radicals is readily derived. Since the spin-spin interaction parameters are typically not observable by transient EPR, the two techniques complement each other favorably. Both EPR methods have recently been applied to a variety of light-induced RPs in photobiology. This review summarizes the results obtained from such studies in the fields of plant and bacterial photosynthesis and DNA repair mediated by the enzyme DNA photolyase.
Tuning the energy band gap of ternary alloyed Cd1-xPbxS quantum dots for photovoltaic applications
NASA Astrophysics Data System (ADS)
Badawi, Ali
2016-02-01
Tuning the energy band gap of ternary alloyed Cd1-xPbxS (x: 0, 0.33, 0.5, 0.67 and 1) quantum dots (QDs) for photovoltaic applications is studied. Alloyed Cd1-xPbxS QDs were adsorbed onto TiO2 nanoparticles (NPs) using ssuccessive ionic layer adsorption and reaction (SILAR) methode. EDX measurements ensure the success adsorption of alloyed Cd1-xPbxS QDs onto the TiO2 electrode. At 100 mW/cm2 (AM 1.5) sun illumination, the photovoltaic performance of alloyed Cd1-xPbxS QDs sensitized solar cells (QDSSCs) was measured. The maximum values of Jsc (1.92 mA/cm2) and η (0.36%) for the alloyed Cd1-xPbxS QDSSCs were obtained when the molar ratio of Cd/Pb is 0.33/0.67. the open circuit voltage (Voc) is equal 0.61 ± 0.01 V for all alloyed Cd1-xPbxS QDSSCs. The electron back recombination rates decrease considerably for alloyed Cd1-xPbxS QDSSCs as x value increases, peaking at 0.67. The electron lifetime (τ) for Cd0.33Pb0.67S QDSSCs is one order of magnitude larger than that of the other alloyed Cd1-xPbxS QDSSCs with different x value. Under ON-OFF cycles to solar illumination, the open circuit voltage decay measurements show the high sensitivity and reproducibility of alloyed Cd1-xPbxS QDSSCs.
Electrically detected magnetic resonance in a W-band microwave cavity
NASA Astrophysics Data System (ADS)
Lang, V.; Lo, C. C.; George, R. E.; Lyon, S. A.; Bokor, J.; Schenkel, T.; Ardavan, A.; Morton, J. J. L.
2011-03-01
We describe a low-temperature sample probe for the electrical detection of magnetic resonance in a resonant W-band (94 GHz) microwave cavity. The advantages of this approach are demonstrated by experiments on silicon field-effect transistors. A comparison with conventional low-frequency measurements at X-band (9.7 GHz) on the same devices reveals an up to 100-fold enhancement of the signal intensity. In addition, resonance lines that are unresolved at X-band are clearly separated in the W-band measurements. Electrically detected magnetic resonance at high magnetic fields and high microwave frequencies is therefore a very sensitive technique for studying electron spins with an enhanced spectral resolution and sensitivity.
EPR spectroscopy of complex biological iron-sulfur systems.
Hagen, Wilfred R
2018-02-21
From the very first discovery of biological iron-sulfur clusters with EPR, the spectroscopy has been used to study not only purified proteins but also complex systems such as respiratory complexes, membrane particles and, later, whole cells. In recent times, the emphasis of iron-sulfur biochemistry has moved from characterization of individual proteins to the systems biology of iron-sulfur biosynthesis, regulation, degradation, and implications for human health. Although this move would suggest a blossoming of System-EPR as a specific, non-invasive monitor of Fe/S (dys)homeostasis in whole cells, a review of the literature reveals limited success possibly due to technical difficulties in adherence to EPR spectroscopic and biochemical standards. In an attempt to boost application of System-EPR the required boundary conditions and their practical applications are explicitly and comprehensively formulated.
Local band gap measurements by VEELS of thin film solar cells.
Keller, Debora; Buecheler, Stephan; Reinhard, Patrick; Pianezzi, Fabian; Pohl, Darius; Surrey, Alexander; Rellinghaus, Bernd; Erni, Rolf; Tiwari, Ayodhya N
2014-08-01
This work presents a systematic study that evaluates the feasibility and reliability of local band gap measurements of Cu(In,Ga)Se2 thin films by valence electron energy-loss spectroscopy (VEELS). The compositional gradients across the Cu(In,Ga)Se2 layer cause variations in the band gap energy, which are experimentally determined using a monochromated scanning transmission electron microscope (STEM). The results reveal the expected band gap variation across the Cu(In,Ga)Se2 layer and therefore confirm the feasibility of local band gap measurements of Cu(In,Ga)Se2 by VEELS. The precision and accuracy of the results are discussed based on the analysis of individual error sources, which leads to the conclusion that the precision of our measurements is most limited by the acquisition reproducibility, if the signal-to-noise ratio of the spectrum is high enough. Furthermore, we simulate the impact of radiation losses on the measured band gap value and propose a thickness-dependent correction. In future work, localized band gap variations will be measured on a more localized length scale to investigate, e.g., the influence of chemical inhomogeneities and dopant accumulations at grain boundaries.
High-Power X-Band Semiconductor RF Switch for Pulse Compression Systems of Future Colliders
NASA Astrophysics Data System (ADS)
Tantawi, Sami G.; Tamura, Fumihiko
2000-04-01
We describe the potential of semiconductor X-band RF switch arrays as a means of developing high power RF pulse compression systems for future linear colliders. The switch systems described here have two designs. Both designs consist of two 3dB hybrids and active modules. In the first design the module is composed of a cascaded active phase shifter. In the second design the module uses arrays of SPST (Single Pole Single Throw) switches. Each cascaded element of the phase shifter and the SPST switch has similar design. The active element consists of symmetrical three-port tee-junctions and an active waveguide window in the symmetrical arm of the tee-junction. The design methodology of the elements and the architecture of the whole switch system are presented. We describe the scaling law that governs the relation between power handling capability and number of elements. The design of the active waveguide window is presented. The waveguide window is a silicon wafer with an array of four hundred PIN/NIP diodes covering the surface of the window. This waveguide window is located in an over-moded TE01 circular waveguide. The results of high power RF measurements of the active waveguide window are presented. The experiment is performed at power levels of tens of megawatts at X-band.
X-Band, 17-Watt Solid-State Power Amplifier
NASA Technical Reports Server (NTRS)
Mittskus, Anthony; Stone, Ernest; Boger, William; Burgess, David; Honda, Richard; Nuckolls, Carl
2005-01-01
An advanced solid-state power amplifier that can generate an output power of as much as 17 W at a design operating frequency of 8.4 GHz has been designed and constructed as a smaller, lighter, less expensive alternative to traveling-wave-tube X-band amplifiers and to prior solid-state X-band power amplifiers of equivalent output power. This amplifier comprises a monolithic microwave integrated circuit (MMIC) amplifier module and a power-converter module integrated into a compact package (see Figure 1). The amplifier module contains an input variable-gain amplifier (VGA), an intermediate driver stage, a final power stage, and input and output power monitors (see Figure 2). The VGA and the driver amplifier are 0.5-m GaAs-based metal semiconductor field-effect transistors (MESFETs). The final power stage contains four parallel high-efficiency, GaAs-based pseudomorphic high-electron-mobility transistors (PHEMTs). The gain of the VGA is voltage-variable over a range of 10 to 24 dB. To provide for temperature compensation of the overall amplifier gain, the gain-control voltage is generated by an operational-amplifier circuit that includes a resistor/thermistor temperature-sensing network. The driver amplifier provides a gain of 14 dB to an output power of 27 dBm to drive the four parallel output PHEMTs, each of which is nominally capable of putting out as much as 5 W. The driver output is sent to the input terminals of the four parallel PHEMTs through microstrip power dividers; the outputs of these PHEMTs are combined by microstrip power combiners (which are similar to the microstrip power dividers) to obtain the final output power of 17 W.
Fluorinated graphene oxide for enhanced S and X-band microwave absorption
DOE Office of Scientific and Technical Information (OSTI.GOV)
Sudeep, P. M.; TIFR-Centre for Interdisciplinary Sciences, Tata Institute of Fundamental Research, Hyderabad 500075; Vinayasree, S.
2015-06-01
Here we report the microwave absorbing properties of three graphene derivatives, namely, graphene oxide (GO), fluorinated GO (FGO, containing 5.6 at. % Fluorine (F)), and highly FGO (HFGO, containing 23 at. % F). FGO is known to be exhibiting improved electrochemical and electronic properties when compared to GO. Fluorination modifies the dielectric properties of GO and hence thought of as a good microwave absorber. The dielectric permittivities of GO, FGO, and HFGO were estimated in the S (2 GHz to 4 GHz) and X (8 GHz to 12 GHz) bands by employing cavity perturbation technique. For this, suspensions containing GO/FGO/HFGO were made in N-Methylmore » Pyrrolidone (NMP) and were subjected to cavity perturbation. The reflection loss was then estimated and it was found that −37 dB (at 3.2 GHz with 6.5 mm thickness) and −31 dB (at 2.8 GHz with 6 mm thickness) in the S band and a reflection loss of −18 dB (at 8.4 GHz with 2.5 mm thickness) and −10 dB (at 11 GHz with 2 mm thickness) in the X band were achieved for 0.01 wt. % of FGO and HFGO in NMP, respectively, suggesting that these materials can serve as efficient microwave absorbers even at low concentrations.« less
Nanoscale measurements of unoccupied band dispersion in few-layer graphene.
Jobst, Johannes; Kautz, Jaap; Geelen, Daniël; Tromp, Rudolf M; van der Molen, Sense Jan
2015-11-26
The properties of any material are fundamentally determined by its electronic band structure. Each band represents a series of allowed states inside a material, relating electron energy and momentum. The occupied bands, that is, the filled electron states below the Fermi level, can be routinely measured. However, it is remarkably difficult to characterize the empty part of the band structure experimentally. Here, we present direct measurements of unoccupied bands of monolayer, bilayer and trilayer graphene. To obtain these, we introduce a technique based on low-energy electron microscopy. It relies on the dependence of the electron reflectivity on incidence angle and energy and has a spatial resolution ∼10 nm. The method can be easily applied to other nanomaterials such as van der Waals structures that are available in small crystals only.
Nanoscale measurements of unoccupied band dispersion in few-layer graphene
Jobst, Johannes; Kautz, Jaap; Geelen, Daniël; Tromp, Rudolf M.; van der Molen, Sense Jan
2015-01-01
The properties of any material are fundamentally determined by its electronic band structure. Each band represents a series of allowed states inside a material, relating electron energy and momentum. The occupied bands, that is, the filled electron states below the Fermi level, can be routinely measured. However, it is remarkably difficult to characterize the empty part of the band structure experimentally. Here, we present direct measurements of unoccupied bands of monolayer, bilayer and trilayer graphene. To obtain these, we introduce a technique based on low-energy electron microscopy. It relies on the dependence of the electron reflectivity on incidence angle and energy and has a spatial resolution ∼10 nm. The method can be easily applied to other nanomaterials such as van der Waals structures that are available in small crystals only. PMID:26608712
The broad-band X-ray spectral variability of Mrk 841
NASA Technical Reports Server (NTRS)
George, I. M.; Nandra, K.; Fabian, A. C.; Turner, T. J.; Done, C.; Day, C. S. R.
1993-01-01
A detailed spectral analysis of five X-ray observations of Mrk 841 with the EXOSAT, Ginga, and ROSAT satellites is reported. Variability is apparent in both the soft (0.1-1.0 keV) and medium (1-20 keV) energy bands. Above, 1 keV, the spectra are adequately modeled by a power law with a strong emission line of equivalent width 450 eV. The large equivalent width of the emission line indicates a strongly enhanced reflection component of the source compared with other Seyferts observed with Ginga. The implications of the results of the analysis for physical models of the emission regions in this and other X-ray bright Seyferts are briefly examined.
Measured reflectance of graded multilayer mirrors designed for astronomical hard X-ray telescopes
NASA Astrophysics Data System (ADS)
Christensen, F. E.; Craig, W. W.; Windt, D. L.; Jimenez-Garate, M. A.; Hailey, C. J.; Harrison, F. A.; Mao, P. H.; Chakan, J. M.; Ziegler, E.; Honkimaki, V.
2000-09-01
Future astronomical X-ray telescopes, including the balloon-borne High-Energy Focusing Telescope (HEFT) and the Constellation-X Hard X-ray Telescope (Con-X HXT) plan to incorporate depth-graded multilayer coatings in order to extend sensitivity into the hard X-ray (10<~E<~80keV) band. In this paper, we present measurements of the reflectance in the 18-170 keV energy range of a cylindrical prototype nested optic taken at the European Synchrotron Radiation Facility (ESRF). The mirror segments, mounted in a single bounce stack, are coated with depth-graded W/Si multilayers optimized for broadband performance up to 69.5 keV (WK-edge). These designs are ideal for both the HEFT and Con-X HXT applications. We compare the measurements to model calculations to demonstrate that the reflectivity can be well described by the intended power law distribution of the bilayer thicknesses, and that the coatings are uniform at the 5% level over the mirror surface. Finally, we apply the measurements to predict effective areas achievable for HEFT and Con-X HXT using these W/Si designs.
Measuring the band structures of periodic beams using the wave superposition method
NASA Astrophysics Data System (ADS)
Junyi, L.; Ruffini, V.; Balint, D.
2016-11-01
Phononic crystals and elastic metamaterials are artificially engineered periodic structures that have several interesting properties, such as negative effective stiffness in certain frequency ranges. An interesting property of phononic crystals and elastic metamaterials is the presence of band gaps, which are bands of frequencies where elastic waves cannot propagate. The presence of band gaps gives this class of materials the potential to be used as vibration isolators. In many studies, the band structures were used to evaluate the band gaps. The presence of band gaps in a finite structure is commonly validated by measuring the frequency response as there are no direct methods of measuring the band structures. In this study, an experiment was conducted to determine the band structure of one dimension phononic crystals with two wave modes, such as a bi-material beam, using the frequency response at only 6 points to validate the wave superposition method (WSM) introduced in a previous study. A bi-material beam and an aluminium beam with varying geometry were studied. The experiment was performed by hanging the beams freely, exciting one end of the beams, and measuring the acceleration at consecutive unit cells. The measured transfer function of the beams agrees with the analytical solutions but minor discrepancies. The band structure was then determined using WSM and the band structure of one set of the waves was found to agree well with the analytical solutions. The measurements taken for the other set of waves, which are the evanescent waves in the bi-material beams, were inaccurate and noisy. The transfer functions at additional points of one of the beams were calculated from the measured band structure using WSM. The calculated transfer function agrees with the measured results except at the frequencies where the band structure was inaccurate. Lastly, a study of the potential sources of errors was also conducted using finite element modelling and the errors in
Gagnon, Derek M.; Brophy, Megan Brunjes; Bowman, Sarah E. J.; Stich, Troy A.; Drennan, Catherine L.; Britt, R. David; Nolan, Elizabeth M.
2015-01-01
The antimicrobial protein calprotectin (CP), a hetero-oligomer of the S100 family members S100A8 and S100A9, is the only identified mammalian Mn(II)-sequestering protein. Human CP uses Ca(II) ions to tune its Mn(II) affinity at a biologically unprecedented hexahistidine site that forms at the S100A8/S100A9 interface, and the molecular basis for this phenomenon requires elucidation. Herein, we investigate the remarkable Mn(II) coordination chemistry of human CP using X-ray crystallography as well as continuous wave (CW) and pulse electron paramagnetic resonance (EPR) spectroscopies. An X-ray crystallographic structure of Mn(II)-CP containing one Mn(II), two Ca(II), and two Na(I) ions per CP heterodimer is reported. The CW EPR spectrum of Ca(II)- and Mn(II)-bound CP prepared with a 10:0.9:1 Ca(II):Mn(II):CP ratio is characterized by an unusually low zero-field splitting of 485 MHz (E/D = 0.30) for the S = 5/2 Mn(II) ion, consistent with the high symmetry of the His6 binding site observed crystallographically. Results from electron spin-echo envelope modulation and electron nuclear double resonance experiments reveal that the six Mn(II)-coordinating histidine residues of Ca(II)- and Mn(II)-bound CP are spectroscopically equivalent. The observed 15N (I = 1/2) hyperfine couplings (A) arise from two distinct classes of nitrogen atoms: the coordinating ε-nitrogen of the imidazole ring of each histidine ligand (A = [3.45, 3.71, 5.91] MHz) and the distal δ-nitrogen (A = [0.11, 0.18, 0.42] MHz). In the absence of Ca(II), the binding affinity of CP for Mn(II) drops by ca. two orders of magnitude and coincides with Mn(II) binding at the His6 site as well as other sites. This study demonstrates the role of Ca(II) in enabling high-affinity and specific binding of Mn(II) to the His6 site of human calprotectin. PMID:25597447
In vivo EPR extracellular pH-metry in tumors using a triphosphonated trityl radical.
Marchand, Valérie; Levêque, Philippe; Driesschaert, Benoit; Marchand-Brynaert, Jacqueline; Gallez, Bernard
2017-06-01
The ability to assess the extracellular pH (pHe) is an important issue in oncology, because extracellular acidification is associated with tumor aggressiveness and resistance to cytotoxic therapies. In this study, a stable triphosphonated triarylmethyl (TPTAM) radical was qualified as a pHe electron paramagnetic resonance (EPR) molecular reporter. Calibration of hyperfine splitting as a function of pH was performed using a 1.2-GHz EPR spectrometer. Gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) was used as an extracellular paramagnetic broadening agent to assess the localization of TPTAM when incubated with cells. In vivo EPR pH-metry was performed in MDA, SiHa, and TLT tumor models and in muscle. Bicarbonate therapy was used to modulate the tumor pHe. EPR measurements were compared with microelectrode readouts. The hyperfine splitting of TPTAM was strongly pH-dependent around the pKa of the probe (pKa = 6.99). Experiments with Gd-DTPA demonstrated that TPTAM remained in the extracellular compartment. pHe was found to be more acidic in the MDA, SiHa, and TLT tumor models compared with muscle. Treatment of animals by bicarbonate induced an increase in pHe in tumors: similar variations in pHe were found when using in vivo EPR or invasive microelectrodes measurements. This study demonstrates the potential usefulness of TPTAM for monitoring pHe in tumors. Magn Reson Med 77:2438-2443, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.
DSN 100-meter X and S band microwave antenna design and performance
NASA Technical Reports Server (NTRS)
Williams, W. F.
1978-01-01
The RF performance is studied for large reflector antenna systems (100 meters) when using the high efficiency dual shaped reflector approach. An altered phase was considered so that the scattered field from a shaped surface could be used in the JPL efficiency program. A new dual band (X-S) microwave feed horn was used in the shaping calculations. A great many shaping calculations were made for various horn sizes and locations and final RF efficiencies are reported. A conclusion is reached that when using the new dual band horn, shaping should probably be performed using the pattern of the lower frequency
Polymer therapeutics and the EPR effect.
Maeda, Hiroshi
History of the EPR (enhanced permeability and retention) effect is discussed, which goes back to the analyses of molecular pathology in bacterial infection and edema (extravasation) formation. The first mediator we found for extravasation was bradykinin. Later on, were found nitric oxide and superoxide, then formation of peroxynitrite, that activates procollagenase. In this inflammatory setting many other vascular mediators are involved that are also common to cancer vasculature. Obviously cancer vasculature is defective architechtally, and this makes macromolecular drugs more permeable through the vascular wall. The importance of this pathophysiological event of EPR effect can be applied to macromolecular drug-delivery, or tumor selective delivery, which takes hours to achieve in the primary as well as metastatic tumors, not to mention of the inflamed tissues. The retention of the EPR means that such drugs will be retained in tumor tissues more than days to weeks. This was demonstrated initially, and most dramatically, using SMANCS, a protein-polymer conjugated-drug dissolved in lipid contrast medium (Lipiodol) by administering intraarterially. For disseminating the EPR concept globally, or in the scientific community, Professor Ruth Duncan played a key role at the early stage, as she worked extensively on polymer- therapeutics, and knew its importance.
Digital Detection and Processing of Multiple Quadrature Harmonics for EPR Spectroscopy
Ahmad, R.; Som, S.; Kesselring, E.; Kuppusamy, P.; Zweier, J.L.; Potter, L.C.
2010-01-01
A quadrature digital receiver and associated signal estimation procedure are reported for L-band electron paramagnetic resonance (EPR) spectroscopy. The approach provides simultaneous acquisition and joint processing of multiple harmonics in both in-phase and out-of-phase channels. The digital receiver, based on a high-speed dual-channel analog-to-digital converter, allows direct digital down-conversion with heterodyne processing using digital capture of the microwave reference signal. Thus, the receiver avoids noise and nonlinearity associated with analog mixers. Also, the architecture allows for low-Q anti-alias filtering and does not require the sampling frequency to be time-locked to the microwave reference. A noise model applicable for arbitrary contributions of oscillator phase noise is presented, and a corresponding maximum-likelihood estimator of unknown parameters is also reported. The signal processing is applicable for Lorentzian lineshape under nonsaturating conditions. The estimation is carried out using a convergent iterative algorithm capable of jointly processing the in-phase and out-of-phase data in the presence of phase noise and unknown microwave phase. Cramér-Rao bound analysis and simulation results demonstrate a significant reduction in linewidth estimation error using quadrature detection, for both low and high values of phase noise. EPR spectroscopic data are also reported for illustration. PMID:20971667
Time-resolved EPR spectroscopy in a Unix environment.
Lacoff, N M; Franke, J E; Warden, J T
1990-02-01
A computer-aided time-resolved electron paramagnetic resonance (EPR) spectrometer implemented under version 2.9 BSD Unix was developed by interfacing a Varian E-9 EPR spectrometer and a Biomation 805 waveform recorder to a PDP-11/23A minicomputer having MINC A/D and D/A capabilities. Special problems with real-time data acquisition in a multiuser, multitasking Unix environment, addressing of computer main memory for the control of hardware devices, and limitation of computer main memory were resolved, and their solutions are presented. The time-resolved EPR system and the data acquisition and analysis programs, written entirely in C, are described. Furthermore, the benefits of utilizing the Unix operating system and the C language are discussed, and system performance is illustrated with time-resolved EPR spectra of the reaction center cation in photosystem 1 of green plant photosynthesis.
Surface Electrostatics of Lipid Bilayers by EPR of a pH-Sensitive Spin-Labeled Lipid
Voinov, Maxim A.; Rivera-Rivera, Izarys; Smirnov, Alex I.
2013-01-01
Many biophysical processes such as insertion of proteins into membranes and membrane fusion are governed by bilayer electrostatic potential. At the time of this writing, the arsenal of biophysical methods for such measurements is limited to a few techniques. Here we describe a, to our knowledge, new spin-probe electron paramagnetic resonance (EPR) approach for assessing the electrostatic surface potential of lipid bilayers that is based on a recently synthesized EPR probe (IMTSL-PTE) containing a reversibly ionizable nitroxide tag attached to the lipids’ polar headgroup. EPR spectra of the probe directly report on its ionization state and, therefore, on electrostatic potential through changes in nitroxide magnetic parameters and the degree of rotational averaging. Further, the lipid nature of the probe provides its full integration into lipid bilayers. Tethering the nitroxide moiety directly to the lipid polar headgroup defines the location of the measured potential with respect to the lipid bilayer interface. Electrostatic surface potentials measured by EPR of IMTSL-PTE show a remarkable (within ±2%) agreement with the Gouy-Chapman theory for anionic DMPG bilayers in fluid (48°C) phase at low electrolyte concentration (50 mM) and in gel (17°C) phase at 150-mM electrolyte concentration. This agreement begins to diminish for DMPG vesicles in gel phase (17°C) upon varying electrolyte concentration and fluid phase bilayers formed from DMPG/DMPC and POPG/POPC mixtures. Possible reasons for such deviations, as well as the proper choice of an electrostatically neutral reference interface, have been discussed. Described EPR method is expected to be fully applicable to more-complex models of cellular membranes. PMID:23332063
Few-femtosecond time-resolved measurements of X-ray free-electron lasers.
Behrens, C; Decker, F-J; Ding, Y; Dolgashev, V A; Frisch, J; Huang, Z; Krejcik, P; Loos, H; Lutman, A; Maxwell, T J; Turner, J; Wang, J; Wang, M-H; Welch, J; Wu, J
2014-04-30
X-ray free-electron lasers, with pulse durations ranging from a few to several hundred femtoseconds, are uniquely suited for studying atomic, molecular, chemical and biological systems. Characterizing the temporal profiles of these femtosecond X-ray pulses that vary from shot to shot is not only challenging but also important for data interpretation. Here we report the time-resolved measurements of X-ray free-electron lasers by using an X-band radiofrequency transverse deflector at the Linac Coherent Light Source. We demonstrate this method to be a simple, non-invasive technique with a large dynamic range for single-shot electron and X-ray temporal characterization. A resolution of less than 1 fs root mean square has been achieved for soft X-ray pulses. The lasing evolution along the undulator has been studied with the electron trapping being observed as the X-ray peak power approaches 100 GW.
NASA Astrophysics Data System (ADS)
Casey, J. A.; Beckers, J. F.; Brossier, E.; Haas, C.
2013-12-01
Operational ice information services rely heavily on space-borne synthetic aperture radar (SAR) data for the production of ice charts to meet their mandate of providing timely and accurate sea ice information to support safe and efficient marine operations. During the summer melt period, the usefulness of SAR data for sea ice monitoring is limited by the presence of wet snow and melt ponds on the ice surface, which can mask the signature of the underlying ice. This is a critical concern for ice services whose clients (e.g. commercial shipping, cruise tourism, resource exploration and extraction) are most active at this time of year when sea ice is at its minimum extent, concentration and thickness. As a result, there is a need to further quantify the loss of ice information in SAR data during the melt season and to identify what information can still be retrieved about ice surface conditions and melt pond evolution at this time of year. To date the majority of studies have been limited to analysis of single-polarization C-band SAR data. This study will investigate the potential complimentary and unique sea ice information that polarimetric C- and X-band SAR data can provide to supplement the information available from traditional single co-polarized C-band SAR data. A time-series of polarimetric C- and X-band SAR data was acquired over Jones Sound in the Canadian Arctic Archipelago, in the vicinity of the Grise Fiord, Nunavut. Five RADARSAT-2 Wide Fine Quad-pol images and 11 TerraSAR-X StripMap dual-pol (HH/VV) images were acquired. The time-series begins at the onset of melt in early June and extends through advanced melt conditions in late July. Over this period several ponding and drainage events and two snowfall events occurred. Field observations of sea ice properties were collected using an Ice Mass Balance (IMB) buoy, hourly photos from a time-lapse camera deployed on a coastal cliff, and manual in situ measurements of snow thickness and melt pond depth
Essential Ambiguity and Essential Influence: Rereading Bohr's Reply to EPR
NASA Astrophysics Data System (ADS)
Plotnitsky, Arkady
2006-01-01
The article offers a rereading of Bohr's reply to the argument of A. Einstein, B. Podolsky, and N. Rosen (EPR) concerning the incompleteness, or else nonlocality, of quantum mechanics. Bohr shows EPR's argument to be deficient on their own terms, by virtue of an ambiguity found in their application of the criterion of reality they propose to the phenomena in question. He also offers an alternative interpretation of the EPR experiment itself, the thought experiment proposed by EPR, as part of his overall interpretation of quantum mechanics as complementarity.
Band Anticrossing in Highly Mismatched Compound Semiconductor Alloys
NASA Technical Reports Server (NTRS)
Yu, Kin Man; Wu, J.; Walukiewicz, W.; Ager, J. W.; Haller, E. E.; Miotkowski, I.; Ramdas, A.; Su, Ching-Hua; Whitaker, Ann F. (Technical Monitor)
2001-01-01
Compound semiconductor alloys in which metallic anions are partially replaced with more electronegative isoelectronic atoms have recently attracted significant attention. Group IIIN(x)V(1-x), alloys with a small amount of the electronegative N substituting more metallic column V elements has been the most extensively studied class of such Highly Mismatched Alloys (HMAs). We have shown that many of the unusual properties of the IIIN(x),V(1-x) alloys can be well explained by the Band Anticrossing (BAC) model that describes the electronic structure in terms of an interaction between highly localized levels of substitutional N and the extended states of the host semiconductor matrix. Most recently the BAC model has been also used to explain similar modifications of the electronic band structure observed in Te-rich ZnS(x)Te(l-x) and ZnSe(Y)Te(1-y) alloys. To date studies of HMAs have been limited to materials with relatively small concentrations of highly electronegative atoms. Here we report investigations of the electronic structure of ZnSe(y)Te(1-y) alloys in the entire composition range, 0 less than or equal to y less than or equal to 1. The samples used in this study are bulk ZnSe(y)Te(1-y) crystals grown by either a modified Bridgman method or by physical vapor transport. Photomodulated reflection (PR) spectroscopy was used to measure the composition dependence of optical transitions from the valence band edge and from the spin-orbit split off band to the conduction band. The pressure dependence of the band gap was measured using optical absorption in a diamond anvil cell. We find that the energy of the spin-orbit split off valence band edge does not depend on composition and is located at about 3 eV below the conduction band edge of ZnSe. On the Te-rich side the pressure and the composition dependence of the optical transitions are well explained by the BAC model which describes the downward shift of the conduction band edge in terms of the interaction between
Li, Jing; Liu, Baodan; Wu, Aimin; Yang, Bing; Yang, Wenjin; Liu, Fei; Zhang, Xinglai; An, Vladimir; Jiang, Xin
2018-05-07
Photoelectrochemical water splitting has emerged as an effective artificial photosynthesis technology to generate clean energy of H 2 from sunlight. The core issue in this reaction system is to develop a highly efficient photoanode with a large fraction of solar light absorption and greater active surface area. In this work, we take advantage of energy band engineering to synthesize (GaN) 1- x (ZnO) x solid solution nanowires with ZnO contents ranging from 10.3% to 47.6% and corresponding band gap tailoring from 3.08 to 2.77 eV on the basis of the Au-assisted VLS mechanism. The morphology of nanowires directly grown on the conductive substrate facilitates the charge transfer and simultaneously improves the surface reaction sites. As a result, a photocurrent approximately 10 times larger than that for a conventional powder-based photoanode is obtained, which indicates the potential of (GaN) 1- x (ZnO) x nanowires in the preparation of superior photoanodes for enhanced water splitting. It is anticipated that the water-splitting capability of (GaN) 1- x (ZnO) x nanowire can be further increased through alignment control for enhanced visible light absorption and reduction of charge transfer resistance.
NASA Astrophysics Data System (ADS)
Prabakaran, R.; Subramanian, P.
2018-04-01
Single crystals of L-histidine-4-nitrophenolate 4-nitrophenol[LHFNP] complex doped with Mn2+ were grown by the slow evaporation method at room temperature. The EPR spectrum reveals the entry of one Mn2+ ion in the lattice. The angular variation plot was drawn between the angles and the magnetic field position. The spin Hamiltonian parameters were obtained by EPR-NMR program. The D and E values show the rhombic field around the ion and is an interstitial one. The g value obtained here suggests that the Mn2+ ion experiences a strong field and there is a transfer of electron from the metal ion to the ligand atom. The optical absorption study shows various bands and are assigned to the transition from the ground state 6A1g(S). The Racah and crystal field parameters have also been evaluated and fitted to the experimental values. The Racah parameter shows the covalent bonding between the metal ion to the ligand.
Various approaches in EPR identification of gamma-irradiated plant foodstuffs: A review.
Aleksieva, Katerina I; Yordanov, Nicola D
2018-03-01
Irradiation of food in the world is becoming a preferred method for their sterilization and extending their shelf life. For the purpose of trade with regard to the rights of consumers is necessary marking of irradiated foodstuffs, and the use of appropriate methods for unambiguous identification of radiation treatment. One-third of the current standards of the European Union to identify irradiated foods use the method of the Electron Paramagnetic Resonance (EPR) spectroscopy. On the other hand the current standards for irradiated foods of plant origin have some weaknesses that led to the development of new methodologies for the identification of irradiated food. New approaches for EPR identification of radiation treatment of herbs and spices when the specific signal is absent or disappeared after irradiation are discussed. Direct EPR measurements of dried fruits and vegetables and different pretreatments for fresh samples are reviewed. Copyright © 2017 Elsevier Ltd. All rights reserved.
NASA Astrophysics Data System (ADS)
Anagnostou, Marios N.; Kalogiros, John; Marzano, Frank S.; Anagnostou, Emmanouil N.; Baldini, Luca; Nikolopoulos, EfThymios; Montopoli, Mario; Picciotti, Errico
2014-05-01
The Mediterranean area concentrates the major natural risks related to the water cycle, including heavy precipitation and flash-flooding during the fall season. Every year in central and south Europe we witness several fatal and economical disasters from severe storm rainfall triggering Flash Floods, and its impacts are increasing worldwide, but remain very difficult to manage. The spatial scale of flash flood occurrence is such that its vulnerability is often focused on dispersed urbanization, transportation and tourism infrastructures (De Marchi and Scolobig 2012). Urbanized and industrialized areas shows peculiar hydrodynamic and meteo-oceanographic features and they concentrate the highest rates of flash floods and fatal disasters. The main causes of disturbance being littoral urban development and harbor activities, the building of littoral rail- and highways, and the presence of several polluted discharges. All the above mentioned characteristics limit our ability to issue timely flood warnings. Precipitation estimates based on raingauge networks are usually associated with low coverage density, particularly at high altitudes. On the other hand, operational weather radar networks may provide valuable information of precipitation at these regimes but reliability of their estimates is often limited due to retrieval (e.g. variability in the reflectivity-to-rainfall relationship) and spatial extent constrains (e.g. blockage issues, overshooting effects). As a result, we currently lack accurate precipitation estimates over urban complex terrain areas, which essentially means that we lack accurate knowledge of the triggering factor for a number of hazards like flash floods and debris flows/landslides occurring in those areas. A potential solution to overcome sampling as well as retrieval uncertainty limitations of current observational networks might be the use of network of low-power dual-polarization X-band radars as complement to raingauges and gap-filling to
Environment-induced decoherence II. Effect of decoherence on Bell's inequality for an EPR pair
NASA Astrophysics Data System (ADS)
Venugopalan, A.; Kumar, Deepak; Ghosh, R.
1995-02-01
According to Bell's theorem, the degree of correlation between spatially separated measurements on a quantum system is limited by certain inequalities if one assumes the condition of locality. Quantum mechanics predicts that this limit can be exceeded, making it nonlocal. We analyse the effect of an environment modelled by a fluctuating magnetic field on the quantum correlations in an EPR singlet as seen in the Bell inequality. We show that in an EPR setup, the system goes from the usual ‘violation’ of Bell's inequality to a ‘non-violation’ for times larger than a characteristic time scale which is related to the parameters of the fluctuating field. We also look at these inequalities as a function of the spatial separation between the EPR pair.
Castelli, L; Fittipaldi, M; Powell, A K; Gatteschi, D; Sorace, L
2011-08-28
A W-band single-crystal EPR study has been performed on a molecular cluster comprising 19 iron(III) ions bridged by oxo- hydroxide ions, Fe(19), in order to investigate magnetic nanosystems with a behavior in between the one of Magnetic NanoParticles (MNP) and that of Single Molecule Magnets (SMM). The Fe(19) has a disk-like shape: a planar Fe(7) core with a brucite (Mg(OH)(2)) structure enclosed in a "shell" of 12 Fe(III) ions. EPR and magnetic measurements revealed an S = 35/2 ground state with an S = 33/2 excited state lying ∼ 8 K above. The presence of other low-lying excited states was also envisaged. Rhombic Zero Field Splitting (ZFS) tensors were determined, the easy axes lying in the Fe(19) plane for both the multiplets. At particular temperatures and orientations, a partially resolved fine structure could be observed which could not be distinguished in powder spectra, due to orientation disorder. The similarities of the EPR behavior of Fe(19) and MNP, together with the accuracy of single crystal analysis, helped to shed light on spectral features observed in MNP spectra, that is a sharp line at g = 2 and a low intensity transition at g = 4. Moreover, a theoretical analysis has been used to estimate the contribution to the total magnetic anisotropy of core and surface; this latter is crucial in determining the easy axis-type anisotropy, alike that of MNP surface. This journal is © The Royal Society of Chemistry 2011
DOE Office of Scientific and Technical Information (OSTI.GOV)
Raitsimring, A.; Astashkin, A. V.; Enemark, J. H.
2012-12-29
In this work, the experimental conditions and parameters necessary to optimize the long-distance (≥ 60 Å) Double Electron-Electron Resonance (DEER) measurements of biomacromolecules labeled with Gd(III) tags are analyzed. The specific parameters discussed are the temperature, microwave band, the separation between the pumping and observation frequencies, pulse train repetition rate, pulse durations and pulse positioning in the electron paramagnetic resonance spectrum. It was found that: (i) in optimized DEER measurements, the observation pulses have to be applied at the maximum of the EPR spectrum; (ii) the optimal temperature range for Ka-band measurements is 14-17 K, while in W-band the optimalmore » temperatures are between 6-9 K; (iii) W-band is preferable to Ka-band for DEER measurements. Recent achievements and the conditions necessary for short-distance measurements (<15 Å) are also briefly discussed.« less
NASA Astrophysics Data System (ADS)
Li, Chao-Ying; Liu, Shi-Fei; Fu, Jin-Xian
2015-11-01
High-order perturbation formulas for a 3d9 ion in rhombically elongated octahedral was applied to calculate the electron paramagnetic resonance (EPR) parameters (the g factors, gi, and the hyperfine structure constants Ai, i = x, y, z) of the rhombic Cu2+ center in CoNH4PO4.6H2O. In the calculations, the required crystal-field parameters are estimated from the superposition model which enables correlation of the crystal-field parameters and hence the EPR parameters with the local structure of the rhombic Cu2+ center. Based on the calculations, the ligand octahedral (i.e. [Cu(H2O)6]2+ cluster) are found to experience the local bond length variations ΔZ (≈0.213 Å) and δr (≈0.132 Å) along axial and perpendicular directions due to the Jahn-Teller effect. Theoretical EPR parameters based on the above local structure are in good agreement with the observed values; the results are discussed.
High-resolution F T spectrum of A 2 Π r - X 2 Σ + band system of MgCl
NASA Astrophysics Data System (ADS)
Saksena, M. D.; Deo, M. N.; Sunanda, K.; Behere, S. H.; Jadhav, Ashok
2011-03-01
The emission spectrum of the A 2 Π r - X 2 Σ + band system of MgCl molecule (360-380 nm) has been recorded on BOMEM DA8 Fourier transform spectrometer at an apodized resolution of 0.035 cm-1. The spectra have been excited under flowing conditions in a demountable stainless steel hollow cathode lamp (400 V, 250 mA) containing anhydrous MgCl2 and Ar. The resulting spectra are very intense and the 0-0, 1-1, 1-0 bands of A 2 Π 1/2- X 2 Σ + sub-transition and the 0-0 band of A 2 Π 3/2- X 2 Σ + sub-transition have been rotationally analyzed. Improved molecular constants have been derived using a least-squares fit program in which optical data of earlier analyzed 0-1 and 0-2 bands ( A 2 Π 1/2- X 2 Σ +) was also included. The Λ-doubling constants in the v' = 0, 1 levels of the A 2 Π 1/2 sub-state are as expected, i.e. p 1 > p 0, where as it is found that the spin-doubling constants of the v″ = 0, 1 and 2 levels of the ground state X 2 Σ +, decrease with the increase in v, i.e. γ 0 > γ 1 > γ 2. This is indicative of the presence of some nearby state, influencing the spin-doubling.
Wu, Aimin; Li, Jing; Liu, Baodan; Yang, Wenjin; Jiang, Yanan; Liu, Lusheng; Zhang, Xinglai; Xiong, Changmin; Jiang, Xin
2017-02-21
(GaN) 1-x (ZnO) x solid solution has attracted extensive attention due to its feasible band-gap tunability and excellent photocatalytic performance in overall water splitting. However, its potential application in the photodegradation of organic pollutants and environmental processing has rarely been reported. In this study, we developed a rapid synthesis process to fabricate porous (GaN) 1-x (ZnO) x solid solution with a tunable band gap in the range of 2.38-2.76 eV for phenol photodegradation. Under visible-light irradiation, (GaN) 0.75 (ZnO) 0.25 solid solution achieved the highest photocatalytic performance compared to other (GaN) 1-x (ZnO) x solid solutions with x = 0.45, 0.65 and 0.85 due to its higher redox capability and lower lattice deformation. Slight Ag decoration with a content of 1 wt% on the surface of the (GaN) 0.75 (ZnO) 0.25 solid solution leads to a significant enhancement in phenol degradation, with a reaction rate eight times faster than that of pristine (GaN) 0.75 (ZnO) 0.25 . Interestingly, phenol in aqueous solution (10 mg L -1 ) can also be completely degraded within 60 min, even under the direct exposure of sunlight irradiation. The photocurrent response indicates that the enhanced photocatalytic activity of (GaN) 0.75 (ZnO) 0.25 /Ag is directly induced by the improved transfer efficiency of the photogenerated electrons at the interface. The excellent phenol degradation performance of (GaN) 1-x (ZnO) x /Ag further broadens their promising photocatalytic utilization in environmental processing, besides in overall water splitting for hydrogen production.
Late-summer sea ice segmentation with multi-polarisation SAR features in C and X band
NASA Astrophysics Data System (ADS)
Fors, Ane S.; Brekke, Camilla; Doulgeris, Anthony P.; Eltoft, Torbjørn; Renner, Angelika H. H.; Gerland, Sebastian
2016-02-01
In this study, we investigate the potential of sea ice segmentation by C- and X-band multi-polarisation synthetic aperture radar (SAR) features during late summer. Five high-resolution satellite SAR scenes were recorded in the Fram Strait covering iceberg-fast first-year and old sea ice during a week with air temperatures varying around 0 °C. Sea ice thickness, surface roughness and aerial photographs were collected during a helicopter flight at the site. Six polarimetric SAR features were extracted for each of the scenes. The ability of the individual SAR features to discriminate between sea ice types and their temporal consistency were examined. All SAR features were found to add value to sea ice type discrimination. Relative kurtosis, geometric brightness, cross-polarisation ratio and co-polarisation correlation angle were found to be temporally consistent in the investigated period, while co-polarisation ratio and co-polarisation correlation magnitude were found to be temporally inconsistent. An automatic feature-based segmentation algorithm was tested both for a full SAR feature set and for a reduced SAR feature set limited to temporally consistent features. In C band, the algorithm produced a good late-summer sea ice segmentation, separating the scenes into segments that could be associated with different sea ice types in the next step. The X-band performance was slightly poorer. Excluding temporally inconsistent SAR features improved the segmentation in one of the X-band scenes.
NASA Technical Reports Server (NTRS)
Jenniskens, Peter; Laux, Christophe O.
2004-01-01
We report the discovery of the N(2)(+) A-X Meinel band in the 780-840 nm meteor emission from two Leonid meteoroids that were ejected less than 1000 years ago by comet 55P/Tempel-Tuttle. Our analysis indicates that the N(2)(+) molecule is at least an order of magnitude less abundant than expected, possibly as a result of charge transfer reactions with meteoric metal atoms. This new band was found while searching for rovibrational transitions in the X(2)Pi electronic ground state of OH (the OH Meinel band), a potential tracer of water bound to minerals in cometary matter. The electronic A-X transition of OH has been identified in other Leonid meteors. We did not detect this OH Meinel band, which implies that the excited A state is not populated by thermal excitation but by a mechanism that directly produces OH in low vibrational levels of the excited A(2)Sigma state. Ultraviolet dissociation of atmospheric or meteoric water vapor is such a mechanism, as is the possible combustion of meteoric organics.
Implementing a new EPR lineshape parameter for organic radicals in carbonaceous matter.
Bourbin, Mathilde; Du, Yann Le; Binet, Laurent; Gourier, Didier
2013-07-17
Electron Paramagnetic Resonance (EPR) is a non-destructive, non-invasive technique useful for the characterization of organic moieties in primitive carbonaceous matter related to the origin of life. The classical EPR parameters are the peak-to-peak amplitude, the linewidth and the g factor; however, such parameters turn out not to suffice to fully determine a single EPR line. In this paper, we give the definition and practical implementation of a new EPR parameter based on the signal shape that we call the R10 factor. This parameter was originally defined in the case of a single symmetric EPR line and used as a new datation method for organic matter in the field of exobiology. Combined to classical EPR parameters, the proposed shape parameter provides a full description of an EPR spectrum and opens the way to novel applications like datation. Such a parameter is a powerful tool for future EPR studies, not only of carbonaceous matter, but also of any substance which spectrum exhibits a single symmetric line. The paper is a literate program-written using Noweb within the Org-mode as provided by the Emacs editor- and it also describes the full data analysis pipeline that computes the R10 on a real EPR spectrum.
NASA Technical Reports Server (NTRS)
Chackerian, Charles, Jr.; Freedman, R.; Giver, L. P.; Brown, L. R.
2001-01-01
The rotationless transition moment squared for the x(sup 1) sigma (sup +) v=3 (left arrow) v=0 band of CO is measured to be the absolute value of R (sub 3-0) squared = 1.7127(25)x 10(exp -7) Debye squared. This value is about 8.6 percent smaller than the value assumed for HITRAN 2000. The Herman-Wallis intensity factor of this band is F=1+0.01168(11)m+0.0001065(79)m squared. The determination of self-broadening coefficients is improved with the inclusion of line narrowing; self-shifts are also reported.
Optical depth measurements by shadow-band radiometers and their uncertainties.
Alexandrov, Mikhail D; Kiedron, Peter; Michalsky, Joseph J; Hodges, Gary; Flynn, Connor J; Lacis, Andrew A
2007-11-20
Shadow-band radiometers in general, and especially the Multi-Filter Rotating Shadow-band Radiometer (MFRSR), are widely used for atmospheric optical depth measurements. The major programs running MFRSR networks in the United States include the Department of Energy Atmospheric Radiation Measurement (ARM) Program, U.S. Department of Agriculture UV-B Monitoring and Research Program, National Oceanic and Atmospheric Administration Surface Radiation (SURFRAD) Network, and NASA Solar Irradiance Research Network (SIRN). We discuss a number of technical issues specific to shadow-band radiometers and their impact on the optical depth measurements. These problems include instrument tilt and misalignment, as well as some data processing artifacts. Techniques for data evaluation and automatic detection of some of these problems are described.
Band gap and band offset of (GaIn)(PSb) lattice matched to InP
NASA Astrophysics Data System (ADS)
Köhler, F.; Böhm, G.; Meyer, R.; Amann, M.-C.
2005-07-01
Metastable (GaxIn1-x)(PySb1-y) layers were grown on (001) InP substrates by gas source molecular beam epitaxy. Low-temperature photoluminescence spectroscopy was applied to these heterostructures and revealed spatially indirect band-to-band recombination of electrons localized in the InP with holes in the (GaxIn1-x)(PySb1-y). In addition, samples with layer thicknesses larger than 100nm showed direct PL across the band gap of (GaxIn1-x)(PySb1-y). Band-gap energies and band offset energies of (GaxIn1-x)(PySb1-y) relative to InP were derived from these PL data. A strong bowing parameter was observed.
NASA Astrophysics Data System (ADS)
Borup, Morten; Grum, Morten; Linde, Jens Jørgen; Mikkelsen, Peter Steen
2016-08-01
Numerous studies have shown that radar rainfall estimates need to be adjusted against rain gauge measurements in order to be useful for hydrological modelling. In the current study we investigate if adjustment can improve radar rainfall estimates to the point where they can be used for modelling overflows from urban drainage systems, and we furthermore investigate the importance of the aggregation period of the adjustment scheme. This is done by continuously adjusting X-band radar data based on the previous 5-30 min of rain data recorded by multiple rain gauges and propagating the rainfall estimates through a hydraulic urban drainage model. The model is built entirely from physical data, without any calibration, to avoid bias towards any specific type of rainfall estimate. The performance is assessed by comparing measured and modelled water levels at a weir downstream of a highly impermeable, well defined, 64 ha urban catchment, for nine overflow generating rain events. The dynamically adjusted radar data perform best when the aggregation period is as small as 10-20 min, in which case it performs much better than static adjusted radar data and data from rain gauges situated 2-3 km away.
EPR study of free radicals in bread
NASA Astrophysics Data System (ADS)
Yordanov, Nicola D.; Mladenova, Ralitsa
2004-05-01
The features of the recorded EPR spectra of paramagnetic species formed in bread and rusk are reported. The appearance of free radicals in them is only connected with their thermal treatment since the starting materials (flour and grains) exhibit very weak EPR signal. The obtained EPR spectra are complex and indicate that: (i) the relative number of paramagnetic species depends on the temperature and treating time of the raw product; (ii) the g-values are strongly temperature dependent with a tendency to coincide at t≥220 °C. Because of the relatively low (150-220 °C) temperature of thermal treatment, the studied free radicals can be assumed to appear in the course of the browning (Maillard) reaction and not to the carbonization of the material.
Vikram, Deepti S.; Bratasz, Anna; Ahmad, Rizwan; Kuppusamy, Periannan
2015-01-01
Methods currently available for the measurement of oxygen concentrations (oximetry) in viable tissues differ widely from each other in their methodological basis and applicability. The goal of this study was to compare two novel methods, particulate-based electron paramagnetic resonance (EPR) and OxyLite oximetry, in an experimental tumor model. EPR oximetry uses implantable paramagnetic particulates, whereas OxyLite uses fluorescent probes affixed on a fiber-optic cable. C3H mice were transplanted with radiation-induced fibrosarcoma (RIF-1) tumors in their hind limbs. Lithium phthalocyanine (LiPc) microcrystals were used as EPR probes. The pO2 measurements were taken from random locations at a depth of ~3 mm within the tumor either immediately or 48 h after implantation of LiPc. Both methods revealed significant hypoxia in the tumor. However, there were striking differences between the EPR and OxyLite readings. The differences were attributed to the volume of tissue under examination and the effect of needle invasion at the site of measurement. This study recognizes the unique benefits of EPR oximetry in terms of robustness, repeatability and minimal invasiveness. PMID:17705635
NASA Astrophysics Data System (ADS)
Epel, Boris; Kotecha, Mrignayani; Halpern, Howard J.
2017-07-01
The value of any measurement and a fortiori any measurement technology is defined by the reproducibility and the accuracy of the measurements. This implies a relative freedom of the measurement from factors confounding its accuracy. In the past, one of the reasons for the loss of focus on the importance of imaging oxygen in vivo was the difficulty in obtaining reproducible oxygen or pO2 images free from confounding variation. This review will briefly consider principles of electron paramagnetic oxygen imaging and describe how it achieves absolute oxygen measurements. We will provide a summary review of the progress in biomedical EPR imaging, predominantly in cancer biology research, discuss EPR oxygen imaging for cancer treatment and tissue graft assessment for regenerative medicine applications.
AgRISTARS. Supporting research: MARS x-band scatterometer
NASA Technical Reports Server (NTRS)
Ulaby, F. T. (Principal Investigator); Gabel, P. F., Jr.; Brunfeldt, D. R.
1981-01-01
The design, construction, and data collection procedures of the mobile agricultural radar sensor (MARS) x band scatterometer are described. This system is an inexpensive, highly mobile, truck mounted FM-CW radar operating at a center frequency of 10.2 GHz. The antennas, which allow for VV and VH polarizations, are configured in a side looking mode that allows for drive by data collection. This configuration shortens fieldwork time considerably while increasing statistical confidence in the data. Both internal calibration, via a delay line, and external calibration with a Luneberg lens are used to calibrate the instrument in terms of sigma(o). The radar scattering cross section per unit area, sigma(o), is found using the radar equation.
Surface electrostatics of lipid bilayers by EPR of a pH-sensitive spin-labeled lipid.
Voinov, Maxim A; Rivera-Rivera, Izarys; Smirnov, Alex I
2013-01-08
Many biophysical processes such as insertion of proteins into membranes and membrane fusion are governed by bilayer electrostatic potential. At the time of this writing, the arsenal of biophysical methods for such measurements is limited to a few techniques. Here we describe a, to our knowledge, new spin-probe electron paramagnetic resonance (EPR) approach for assessing the electrostatic surface potential of lipid bilayers that is based on a recently synthesized EPR probe (IMTSL-PTE) containing a reversibly ionizable nitroxide tag attached to the lipids' polar headgroup. EPR spectra of the probe directly report on its ionization state and, therefore, on electrostatic potential through changes in nitroxide magnetic parameters and the degree of rotational averaging. Further, the lipid nature of the probe provides its full integration into lipid bilayers. Tethering the nitroxide moiety directly to the lipid polar headgroup defines the location of the measured potential with respect to the lipid bilayer interface. Electrostatic surface potentials measured by EPR of IMTSL-PTE show a remarkable (within ±2%) agreement with the Gouy-Chapman theory for anionic DMPG bilayers in fluid (48°C) phase at low electrolyte concentration (50 mM) and in gel (17°C) phase at 150-mM electrolyte concentration. This agreement begins to diminish for DMPG vesicles in gel phase (17°C) upon varying electrolyte concentration and fluid phase bilayers formed from DMPG/DMPC and POPG/POPC mixtures. Possible reasons for such deviations, as well as the proper choice of an electrostatically neutral reference interface, have been discussed. Described EPR method is expected to be fully applicable to more-complex models of cellular membranes. Copyright © 2013 Biophysical Society. Published by Elsevier Inc. All rights reserved.
Landsat Data Continuity Mission (LDCM) - Optimizing X-Band Usage
NASA Technical Reports Server (NTRS)
Garon, H. M.; Gal-Edd, J. S.; Dearth, K. W.; Sank, V. I.
2010-01-01
The NASA version of the low-density parity check (LDPC) 7/8-rate code, shortened to the dimensions of (8160, 7136), has been implemented as the forward error correction (FEC) schema for the Landsat Data Continuity Mission (LDCM). This is the first flight application of this code. In order to place a 440 Msps link within the 375 MHz wide X band we found it necessary to heavily bandpass filter the satellite transmitter output . Despite the significant amplitude and phase distortions that accompanied the spectral truncation, the mission required BER is maintained at < 10(exp -12) with less than 2 dB of implementation loss. We utilized a band-pass filter designed ostensibly to replicate the link distortions to demonstrate link design viability. The same filter was then used to optimize the adaptive equalizer in the receiver employed at the terminus of the downlink. The excellent results we obtained could be directly attributed to the implementation of the LDPC code and the amplitude and phase compensation provided in the receiver. Similar results were obtained with receivers from several vendors.
Heavy-ion-induced sucrose radicals investigated using EPR and UV spectroscopy
Nakagawa, Kouichi; Karakirova, Yordanka; Yordanov, Nicola D.
2015-01-01
The potential use of a sucrose dosimeter for estimating both linear energy transfer (LET) and the absorbed dose of heavy ion and X-ray radiation was investigated. The stable free radicals were produced when sucrose was irradiated with heavy ions, such as helium, carbon, silicon and neon ions, and when the X-ray radiation was similar to the obtained electron paramagnetic resonance (EPR) spectra, which were ∼7 mT wide and composed of several hyperfine structures. In addition, the total spin concentration resulting from heavy-ion irradiation increased linearly as the absorbed dose increased, and decreased logarithmically as the LET increased. These empirical relations imply that the LET at a certain dose can be determined from the spin concentration. For sucrose and alanine, both cross-sections following C-ion irradiation with a 50 Gy dose were ∼1.3 × 10−12 [μm2], taking into account the molecular size of the samples. The values of these cross-sections imply that multiple ionizing particles were involved in the production of stable radicals. Furthermore, UV absorbance at 267 nm of an aqueous solution of irradiated sucrose was found to linearly increase with increasing absorbed dose. Therefore, the EPR and UV results suggest that sucrose can be a useful dosimeter for heavy-ion irradiation. PMID:25480828
Pressure dependence of band-gap and phase transitions in bulk CuX (X = Cl, Br, I)
DOE Office of Scientific and Technical Information (OSTI.GOV)
Azhikodan, Dilna; Nautiyal, Tashi; Sharma, S.
2016-05-06
Usually a phase transition, in theoretical studies, is explored or verified by studying the total energy as a function of the volume considering various plausible phases. The intersection point, if any, of the free energy vs. volume curves for the different phases is then the indicator of the phase transition(s). The question is, can the theoretical study of a single phase alone indicate a phase transition? i.e. can we look beyond the phase under consideration through such a study? Using density-functional theory, we report a novel approach to suggest phase transition(s) through theoretical study of a single phase. Copper halidesmore » have been engaged for this study. These are direct band-gap semiconductors, with zinc blende structure at ambient conditions, and are reported to exhibit many phase transitions. We show that the study of volume dependence of energy band-gap in a single phase facilitates looking beyond the phase under consideration. This, when translated to pressures, reflects the phase transition pressures for CuX (X = Cl, Br, I) with an encouraging accuracy. This work thus offers a simple, yet reliable, approach based on electronic structure calculations to investigate new semiconducting materials for phase changes under pressure.« less
Vives, Alejandra; Amable, Marcelo; Ferrer, Montserrat; Moncada, Salvador; Llorens, Clara; Muntaner, Carles; Benavides, Fernando G; Benach, Joan
2010-08-01
Despite the fact that labour market flexibility has resulted in an expansion of precarious employment in industrialised countries, to date there is limited empirical evidence concerning its health consequences. The Employment Precariousness Scale (EPRES) is a newly developed, theory-based, multidimensional questionnaire specifically devised for epidemiological studies among waged and salaried workers. To assess the acceptability, reliability and construct validity of EPRES in a sample of waged and salaried workers in Spain. A sample of 6968 temporary and permanent workers from a population-based survey carried out in 2004-2005 was analysed. The survey questionnaire was interviewer administered and included the six EPRES subscales, and measures of the psychosocial work environment (COPSOQ ISTAS21) and perceived general and mental health (SF-36). A high response rate to all EPRES items indicated good acceptability; Cronbach's alpha coefficients, over 0.70 for all subscales and the global score, demonstrated good internal consistency reliability; exploratory factor analysis using principal axis analysis and varimax rotation confirmed the six-subscale structure and the theoretical allocation of all items. Patterns across known groups and correlation coefficients with psychosocial work environment measures and perceived health demonstrated the expected relations, providing evidence of construct validity. Our results provide evidence in support of the psychometric properties of EPRES, which appears to be a promising tool for the measurement of employment precariousness in public health research.
Evaluation of the JPL X-band 32 element active array. [for deep space communication
NASA Technical Reports Server (NTRS)
Boreham, J. F.; Postal, R. B.; Conroy, B. L.
1979-01-01
Tests performed on an X-band 32-element active array are described. Antenna pattern characteristics of the array were tested in its standard operating mode as well as several degraded performance modes, including failures of 1, 2, 3, 4, 8, 16, and 31 elements. Additionally, the array was characterized with the addition of a metallic shroud, and also characterized versus rf drive level and at a single off-axis electronic beamsteered position. Characterization was performed on several of the 3/4-watt, three-stage, X-band solid-state power amplifier modules. The characterization included swept amplitude response, amplitude and phase versus temperature from -20 to +60 C, and intermodulation distortion of selected modules. The array is described and conclusions and recommendations based upon the experience and results achieved are included.
Band Anticrossing in Highly Mismatched Compound Semiconductor Alloys
NASA Technical Reports Server (NTRS)
Yu, Kin Man; Wu, J.; Walukiewicz, W.; Ager, J. W.; Haller, E. E.; Miotkowski, I.; Su, Ching-Hua; Curreri, Peter A. (Technical Monitor)
2001-01-01
Compound semiconductor alloys in which metallic anions are partially replaced with more electronegative isoelectronic atoms have recently attracted significant attention. Group IIIN(sub x)V(sub 1-x) alloys with a small amount of the electronegative N substituting more metallic column V elements has been the most extensively studied class of such Highly Mismatched Alloys (HMAs). We have shown that many of the unusual properties of the IIIN(sub x)V(sub 1-x) alloys can be well explained by the Band Anticrossing (BAC) model that describes the electronic structure in terms of an interaction between highly localized levels of substitutional N and the extended states of the host semiconductor matrix. Most recently the BAC model has been also used to explain similar modifications of the electronic band structure observed in Te-rich ZnS(sub x)Te(sub 1-x) and ZnSe(sub y)Te(sub 1-y) alloys. To date studies of HMAs have been limited to materials with relatively small concentrations of highly electronegative atoms. Here we report investigations of the electronic structure of ZnSe(sub y)Te(sub 1-y) alloys in the entire composition range, y between 0 and 1. The samples used in this study are bulk ZnSe(sub y)Te(sub 1-y) crystals grown by either a modified Bridgman method or by physical vapor transport. Photomodulated reflection (PR) spectroscopy was used to measure the composition dependence of optical transitions from the valence band edge and from the spin-orbit split off band to the conduction band. The pressure dependence of the band gap was measured using optical absorption in a diamond anvil cell. We find that the energy of the spin-orbit split off valence band edge does not depend on composition and is located at about 3 eV below the conduction band edge of ZnSe. On the Te-rich side the pressure and the composition dependence of the optical transitions are well explained by the BAC model which describes the downward shift of the conduction band edge in terms of the
Kawamura, O; Shimoyama, Y; Hosaka, H; Kuribayashi, S; Maeda, M; Nagoshi, A; Zai, H; Kusano, M
2011-05-01
Gastro-esophageal reflux disease (GERD)-related chronic cough (CC) may have multifactorial causes. To clarify the characteristics of esophagopharyngeal reflux (EPR) events in CC patients whose cough was apparently influenced by gastro-esophageal reflux (GER), we studied patients with CC clearly responding to full-dose proton pump inhibitor (PPI) therapy (CC patients). Ten CC patients, 10 GERD patients, and 10 healthy controls underwent 24-h ambulatory pharyngo-esophageal impedance and pH monitoring. Weakly acidic reflux was defined as a decrease of pH by >1 unit with a nadir pH >4. In six CC patients, monitoring was repeated after 8 weeks of PPI therapy. The number of each EPR event and the symptom association probability (SAP) were calculated. Symptoms were evaluated by a validated GERD symptom questionnaire. Weakly acidic gas EPR and swallowing-induced acidic/weakly acidic EPR only occurred in CC patients, and the numbers of such events was significantly higher in the CC group than in the other two groups (P < 0.05, respectively). Symptom association probability analysis revealed a positive association between GER and cough in three CC patients. Proton pump inhibitor therapy abolished swallowing-induced acidic/weakly acidic EPR, reduced weakly acidic gas EPR, and improved symptoms (all P < 0.05). Most patients with CC responding to PPI therapy had weakly acidic gas EPR and swallowing-induced acidic/weakly acidic EPR. A direct effect of acidic mist or liquid refluxing into the pharynx may contribute to chronic cough, while cough may also arise indirectly from reflux via a vago-vagal reflex in some patients. © 2011 Blackwell Publishing Ltd.
Evaluating the Potential of Q-Band ESR Spectroscopy for Dose Reconstruction of Fossil Tooth Enamel
Guilarte, Verónica; Trompier, François; Duval, Mathieu
2016-01-01
The potential of Q-band Electron Spin Resonance (ESR) for quantitative measurements has been scarcely evaluated in the literature and its application for dose reconstruction of fossil tooth enamel with dating purposes remains still quite unknown. Hence, we have performed a comparative study based on several Early to Middle Pleistocene fossil tooth samples using both X- and Q-band spectroscopies. Our results show that Q-band offers a significant improvement in terms of sensitivity and signal resolution: it allows not only to work with reduced amounts of valuable samples (< 4 mg), but also to identify different components of the main composite ESR signal. However, inherent precision of the ESR intensity measurements at Q-band is clearly lower than that achieved at X-band, highlighting the necessity to carry out repeated measurements. All dose values derived from X- and Q-band are nevertheless systematically consistent at either 1 or 2 sigma. In summary, our results indicate that Q-band could now be considered as a reliable tool for ESR dosimetry/dating of fossil teeth although further work is required to improve the repeatability of the measurements. PMID:26930398
The role of halides on a chromium ligand field in lead borate glasses
NASA Astrophysics Data System (ADS)
Sekhar, K. Chandra; Srinivas, B.; Narsimlu, N.; Narasimha Chary, M.; Shareefuddin, Md
2017-10-01
Glasses with a composition of PbX-PbO-B2O3 (X = F2, Cl2 and Br2) containing Cr3+ ions were prepared by a melt quenching technique and investigated by using x-ray diffraction (XRD), optical absorption and electron paramagnetic resonance (EPR) studies. X-ray diffractograms revealed the amorphous nature of the glasses. The density and molar volume were determined. Density values increased for the PFPBCR glass system and decreased for the PCPBCR and PBPBCR glass systems with the composition. Optical absorption spectra were recorded at room temperature (RT) to evaluate the optical band gap E opt and Urbach energies. All the spectra showed characteristic peaks at around 450 nm, 600 nm and 690 nm, and they are assigned to 4 A 2g → 4 T 1g, 4 A 2g → 4 T 2g, 4 A 2g → 2 E transitions respectively. From the optical absorption spectral data, the crystal field (D q ) and Racah parameters (B and C) have been evaluated. Variations in optical band gaps were explained using the electro negativity of halide ions. Electron paramagnetic resonance (EPR) studies were carried out by introducing Cr3+ as the spin probe. The EPR spectra of all the glass samples were recorded at X-band frequencies. The EPR spectra exhibit two resonance signals with effective g values at g ≈ 4.82 and g ≈ 1.99 and are attributed to isolated Cr3+ ions and exchange coupled Cr3+ pairs respectively. The number of spins along with susceptibility are also calculated from the EPR spectra.
Spin entanglement, decoherence and Bohm's EPR paradox.
Cavalcanti, E G; Drummond, P D; Bachor, H A; Reid, M D
2009-10-12
We obtain criteria for entanglement and the EPR paradox for spin-entangled particles and analyse the effects of decoherence caused by absorption and state purity errors. For a two qubit photonic state, entanglement can occur for all transmission efficiencies. In this case, the state preparation purity must be above a threshold value. However, Bohm's spin EPR paradox can be achieved only above a critical level of loss. We calculate a required efficiency of 58%, which appears achievable with current quantum optical technologies. For a macroscopic number of particles prepared in a correlated state, spin entanglement and the EPR paradox can be demonstrated using our criteria for efficiencies eta > 1/3 and eta > 2/3 respectively. This indicates a surprising insensitivity to loss decoherence, in a macroscopic system of ultra-cold atoms or photons.
NASA Astrophysics Data System (ADS)
Hariyadi, T.; Mulyasari, S.; Mukhidin
2018-02-01
In this paper we have designed and simulated a Band Pass Filter (BPF) at X-band frequency. This filter is designed for X-band weather radar application with 9500 MHz center frequency and bandwidth -3 dB is 120 MHz. The filter design was performed using a hairpin microstrip combined with an open stub and defected ground structure (DGS). The substrate used is Rogers RT5880 with a dielectric constant of 2.2 and a thickness of 1.575 mm. Based on the simulation results, it is found that the filter works on frequency 9,44 - 9,56 GHz with insertion loss value at pass band is -1,57 dB.
Merunka, Dalibor; Peric, Miroslav
2017-05-25
Electron paramagnetic resonance (EPR) spectra of radicals in solution depend on their relative motion, which modulates the Heisenberg spin exchange and dipole-dipole interactions between them. To gain information on radical diffusion from EPR spectra demands both reliable spectral fitting to find the concentration coefficients of EPR parameters and valid expressions between the concentration and diffusion coefficients. Here, we measured EPR spectra of the 14 N- and 15 N-labeled perdeuterated TEMPONE radicals in normal and supercooled water at various concentrations. By fitting the EPR spectra to the functions based on the modified Bloch equations, we obtained the concentration coefficients for the spin dephasing, coherence transfer, and hyperfine splitting parameters. Assuming the continuous diffusion model for radical motion, the diffusion coefficients of radicals were calculated from the concentration coefficients using the standard relations and the relations derived from the kinetic equations for the spin evolution of a radical pair. The latter relations give better agreement between the diffusion coefficients calculated from different concentration coefficients. The diffusion coefficients are similar for both radicals, which supports the presented method. They decrease with lowering temperature slower than is predicted by the Stokes-Einstein relation and slower than the rotational diffusion coefficients, which is similar to the diffusion of water molecules in supercooled water.
EPR Oximetry for Investigation of Hyperbaric O2 Pre-treatment for Tumor Radiosensitization.
Williams, Benjamin B; Hou, Huagang; Coombs, Rachel; Swartz, Harold M
A number of studies have reported benefits associated with the application of hyperbaric oxygen treatment (HBO) delivered immediately prior to radiation therapy. While these studies provide evidence that pre-treatment with HBO may be beneficial, no measurements of intratumoral pO2 were carried out and they do not directly link the apparent benefits to decreased hypoxic fractions at the time of radiation therapy. While there is empirical evidence and some theoretical basis for HBO to enhance radiation therapy, without direct and repeated measurements of its effects on pO2, it is unlikely that the use of HBO can be understood and optimized for clinical applications. In vivo EPR oximetry is a technique uniquely capable of providing repeated direct measurements of pO2 through a non-invasive procedure in both animal models and human patients. In order to evaluate the ability of pretreatment with HBO to elevate tumor pO2, a novel small animal hyperbaric chamber system was constructed that allows simultaneous in vivo EPR oximetry. This chamber can be placed within the EPR magnet and is equipped with a variety of ports for multiplace gas delivery, thermoregulation, delivery of anesthesia, physiologic monitoring, and EPR detection. Initial measurements were performed in a subcutaneous RIF-1 tumor model in C3H/HeJ mice. The mean baseline pO2 value was 6.0 ± 1.2 mmHg (N = 7) and responses to two atmospheres absolute pressure HBO varied considerably across subjects, within tumors, and over time. When an increase in pO2 was observed, the effect was transient in all but one case, with durations lasting from 5 min to over 20 min, and returned to baseline levels during HBO administration. These results indicate that without direct measurements of pO2 in the tissue of interest, it is likely to be difficult to know the effects of HBO on actual tissue pO2.
Nightglow emissions of OH/X 2 pi/ - Comparison of theory and measurements in the /9-3/ band
NASA Technical Reports Server (NTRS)
Frederick, J. E.; Rusch, D. W.; Liu, S. C.
1978-01-01
The visible airglow experiments on the Atmosphere Explorer C and E satellites have viewed the (9-3) band nightglow emission of the excited hydroxyl radical in the lower thermosphere at tropical latitudes. The surface brightnesses observed at similar local times vary by approximately a factor of 2. Comparison of the measurements with time-dependent photochemical calculations shows reasonable agreement and indicates that temporal changes in atmospheric transport processes are the most likely explanation of the nightglow variations.
NASA Astrophysics Data System (ADS)
Geldzahler, B.; Birr, R.; Brown, R.; Grant, K.; Hoblitzell, R.; Miller, M.; Woods, G.; Argueta, A.; Ciminera, M.; Cornish, T.; D'Addario, L.; Davarian, F.; Kocz, J.; Lee, D.; Morabito, D.; Tsao, P.; Jakeman-Flores, H.; Ott, M.; Soloff, J.; Denn, G.; Church, K.; Deffenbaugh, P.
2016-09-01
NASA is pursuing a demonstration of coherent uplink arraying at 7.145-7.190 GHz (X-band) and 30-31 GHz (Kaband) using three 12m diameter COTS antennas separated by 60m at the Kennedy Space Center in Florida. In addition, we have used up to three 34m antennas separated by 250m at the Goldstone Deep Space Communication Complex in California at X-band 7.1 GHz incorporating real-time correction for tropospheric phase fluctuations. Such a demonstration can enable NASA to design and establish a high power, high resolution, 24/7 availability radar system for (a) tracking and characterizing observations of Near Earth Objects (NEOs), (b) tracking, characterizing and determining the statistics of small-scale (≤10cm) orbital debris, (c) incorporating the capability into its space communication and navigation tracking stations for emergency spacecraft commanding in the Ka band era which NASA is entering, and (d) fielding capabilities of interest to other US government agencies. We present herein the results of our phased array uplink combining at near 7.17 and 8.3 GHz using widely separated antennas demonstrations at both locales, the results of a study to upgrade from a communication to a radar system, and our vision for going forward in implementing a high performance, low lifecycle cost multi-element radar array.
NASA Astrophysics Data System (ADS)
Hammann, Mark Gregory
The fusion of electro-optical (EO) multi-spectral satellite imagery with Synthetic Aperture Radar (SAR) data was explored with the working hypothesis that the addition of multi-band SAR will increase the land-cover (LC) classification accuracy compared to EO alone. Three satellite sources for SAR imagery were used: X-band from TerraSAR-X, C-band from RADARSAT-2, and L-band from PALSAR. Images from the RapidEye satellites were the source of the EO imagery. Imagery from the GeoEye-1 and WorldView-2 satellites aided the selection of ground truth. Three study areas were chosen: Wad Medani, Sudan; Campinas, Brazil; and Fresno- Kings Counties, USA. EO imagery were radiometrically calibrated, atmospherically compensated, orthorectifed, co-registered, and clipped to a common area of interest (AOI). SAR imagery were radiometrically calibrated, and geometrically corrected for terrain and incidence angle by converting to ground range and Sigma Naught (?0). The original SAR HH data were included in the fused image stack after despeckling with a 3x3 Enhanced Lee filter. The variance and Gray-Level-Co-occurrence Matrix (GLCM) texture measures of contrast, entropy, and correlation were derived from the non-despeckled SAR HH bands. Data fusion was done with layer stacking and all data were resampled to a common spatial resolution. The Support Vector Machine (SVM) decision rule was used for the supervised classifications. Similar LC classes were identified and tested for each study area. For Wad Medani, nine classes were tested: low and medium intensity urban, sparse forest, water, barren ground, and four agriculture classes (fallow, bare agricultural ground, green crops, and orchards). For Campinas, Brazil, five generic classes were tested: urban, agriculture, forest, water, and barren ground. For the Fresno-Kings Counties location 11 classes were studied: three generic classes (urban, water, barren land), and eight specific crops. In all cases the addition of SAR to EO resulted
Investigation of an X-band gigawatt long pulse multi-beam relativistic klystron amplifier
DOE Office of Scientific and Technical Information (OSTI.GOV)
Liu, Zhenbang; Huang, Hua; Lei, Lurong
2015-09-15
To achieve a gigawatt-level long pulse radiation power in X-band, a multi-beam relativistic klystron amplifier is proposed and studied experimentally. By introducing 18 electron drift tubes and extended interaction cavities, the power capacity of the device is increased. A radiation power of 1.23 GW with efficiency of 41% and amplifier gain of 46 dB is obtained in the particle-in-cell simulation. Under conditions of a 10 Hz repeat frequency and an input RF power of 30 kW, a radiation power of 0.9 GW, frequency of 9.405 GHz, pulse duration of 105 ns, and efficiency of 30% is generated in the experiment, and the amplifier gain is aboutmore » 45 dB. Both the simulation and the experiment prove that the multi-beam relativistic klystron amplifier can generate a long pulse GW-level radiation power in X-band.« less
Vives, Alejandra; González, Francisca; Moncada, Salvador; Llorens, Clara; Benach, Joan
2015-01-01
This study examines the psychometric properties of the revised Employment Precariousness Scale (EPRES-2010) in a context of economic crisis and growing unemployment. Data correspond to salaried workers with a contract (n=4,750) from the second Psychosocial Work Environment Survey (Spain, 2010). Analyses included acceptability, scale score distributions, Cronbach's alpha coefficient and exploratory factor analysis. Response rates were 80% or above, scores were widely distributed with reductions in floor effects for temporariness among permanent workers and for vulnerability. Cronbach's alpha coefficients were 0.70 or above; exploratory factor analysis confirmed the theoretical allocation of 21 out of 22 items. The revised version of the EPRES demonstrated good metric properties and improved sensitivity to worker vulnerability and employment instability among permanent workers. Furthermore, it was sensitive to increased levels of precariousness in some dimensions despite decreases in others, demonstrating responsiveness to the context of the economic crisis affecting the Spanish labour market. Copyright © 2015 SESPAS. Published by Elsevier Espana. All rights reserved.